O level Chem Revision

8/6/2019 O level Chem Revision

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SECTION AAnswer the following questions in the spaces provided.1. In what way is each of the following statements false?

(a) Hydrogen chloride is a good conductor of electricity when it is dissolved in any1;~ .. ;...I

(b) One difference between a metal and a non-metal is that a metal can form an ion but anon-metal cannot form an ion.

(184 2A 6)

Fluorine can form either covalent or ionic bonds.(a) Draw a 'dot-and-cross' diagram to show the bonding in

(i) sodium fluoride, NaF,(ii) fluorine, Fz:

(b) Explain why sodium fluoride has a higher melting point than fluorine ..r

I


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7. The incomplete diagram below represents the arrangement of the ions in crystals of eithersodium chloride or magnesium oxide,

. . - _ - - _ - - - - - _ ~ ; t - - - - - - ~ \ \ l a positive ion, Na' or Mg"o a negative ion, CI or 0'

(ii) How does this crystal structure explain the fact that neither sodium chloridenor maznesium oxide conduct an electric current when in the solid state?

(iii) What feature of the ions in the two compounds explains why the melting point

(b) Give a co~e~~ial ~s~-o(~~g~e~i~ ~~id~'hi~hdep~~ds ~~. t h e high 'v~i~e for itsmelting point. C'atn C l - C ! +om.

(N94 P2 A5)


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SECTIONBAnswer the following questions.1. Potassium hydroxide is a typical alkali.

(a) (i) Name another typical alkali.(ii) Give the name and the formula of the negatively charged ions present in aqueous

solutions of alkalis.(b) How, the under what conditions, does excess potassium hydroxide react with:

(i) ammonium chloride, (ii) copper(II) sulphate solution?Write an equation for each reaction.(iii) If the solution from (b) (ii) were filtered, describe the appearance of the filtrate.(iv) How would you show that the filtrate contained sulphate ions?

(c) Give one similarity and one difference between a base and an alkali.(d) A solution of potassium carbonate in water is alkaline. How would you distinguishbetween potassium carbonate and potassium hydroxide?

2. (a) Sodium hydroxide is a typical alkali. Describe how you would neutralise a solutionof sodium hydroxide with dilute hydrochloric acid by the titration method. Write anequation for the reaction.

(b) A solution of sodium hydroxide in water has a pH of 14. Explain fully what youunderstand by the pH scale.

(c) What would you see when sodium hydroxide is added to a solution of(i) universal indicator,(ii) iron(ll) sulphate,(iii) zinc chloride?Name the products of the reaction (c) (ii),

3. (a) Sodium hydroxide is said to be a "typical alkali". Explain what is meant by an alkali,and state two properties which such a substance possesses.

(b) W-hat would you observe if carbon dioxide were bubbled into(i) water containing universal indicator solution,(ii) lime water, until no further change was seen?

(c) Magnesium burns in carbon dioxide to give magnesium oxide and carbon.(i) Describe what you would observe if you carried out this experiment, and write

the equation for the reaction.(ii) How would you separate carbon from the mixture of magnesium oxide and

carbon?(iii) What mass of carbon could be obtained in this reaction using 22 g of carbon

dioxide and an excess of magnesium?

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4. Copper(II) sulphate crystals may be prepared in the way described below. Read thedescription and answer the questions that follow.A small amount ofsolid copper(II) carbonate was added todilute sulphuric acid in abeaker.The mixture was stirred until all the copper(U) carbonate had reacted. This was repeateduntil no more copper(II) carbonate would react. Themixture was filtered into an evapora-ting basin which was warmed until a saturated solution was obtained and then allowed tocool. The crystals produced were filtered off, washed, and dried before being weighed.(a) Describe all that you would see from the time the first sample ofcopper(II) carbonatewas added to the acid until no more would react. Explain how you would know thatall the copper(II) carbonate had reacted.

(b) What is meant by the term saturated solution? Describe one test you would make onthe solution of copper(lI) sulphate to see that itwas saturated before it was allowedto cool.

(c) Describe how you would wash and dry the crystals.(d) Describe a test you would use to show that the crystals contained sulphate ions.(e) The equation for the reaction is

CuC03 + H2S04 4CuS04 +CO2 +H20Given that the relative molecular mass (Mr) ofcopper(II) sulphate crystals is250, whatwould be the mass of copper(II) sulphate produced if 62 g of copper(II) carbonatecompletely reacted with the acid? The actual mass obtained by doing the experimentis less than the calculated amount. Suggest a reason for this.

(f) Why do copper(JI) sulphate crystals lose weight when they are heated?5. (a) Give four different ways inwhichyou could test that a liquid isacidic. Explain ineachcase what you would see that shows the acidity.

(b) Both copper(II) sulphate and sodium sulphate are soluble in water.(i) Describe how you would prepare either of these using dilute sulphuric acid as

one reagent.(ii) Write a chemical equation for the preparation you have described.

6. (a) Describe three chemical reactions of an alkali.Write a chemical equation to represent anyone of these reactions. State symbols arenot required.

(b) When sodium hydroxide solution reacts with a solution of the sulphate ofa particularmetal, a blue precipitate forms. What is the precipitate?Write a chemical equation for the reaction. State symbols are required.

(195 P3 88)7. Most acids have similar chemical reactions. Describe three reactions typical of acids.

Write a chemical equation for one of these reactions. (N97 P3 BIOa)

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8. Ammonium nitrate is a fertilizer. Briefly describe how crystals of ammonium nitrate canbe prepared in a laboratory. Write a chemical equation for the preparation. Include statesymbols. (J98 P3 Bllb)

9. Sulphur dioxide is an acidic oxide.(a) Name two other types of oxide and give an example of each.(b) Explain why sulphur dioxide is classified as an acidic oxide, and why calcium oxide is

not. Write equations to support your explanation. (J99 P3 B9)10. Copper(II) sulphate crystals, CuS04.5HP, are soluble in water.

(a) Describe how these crystals could be prepared from a named dilute acid and a suitablecompound of copper.

(b) Calculate the mass of copper(II) sulphate, CuS04 , contained in 250 em" of a solutionof concentration 2.0 mol / dm'.[A,: Cu, 64; 0, 16; S, 32.] (N99 P3 BI0)

11. (a) Describe how crystals of copper(II) sulphate can be prepared from copper(II) oxideand sulphuric acid. Write the equation for the reaction.

(b) Crystals of copper(II) sulphate have the formula CuS04.5Hp. Calculate thepercentage of water of crystallisation in the crystals.[Relative atomic masses, A r: H, 1; 0, 16; S, 32; Cu, 64] (J2002 P3 BI0)

12. (a) Lime is an alkaline substance. Give two uses of lime that depend on this property.One of the uses must be in farming.

(b) Fig. 12 shows some of the properties ofa calcium compound, O.The letters are not the chemical symbols of the substances.

a calciumcompoundo

adddilute acid

heatstrongly

dissolve inwater

m ix withl imewater

Fig. 12

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(i) Suggest the identity of 0, P, Q and R.(ii) Name an acid that could be used to liberate gas Q from solid O.(iii) Write an equation, including state symbols, for anyone of the reactions shownin Fig. 12. (12003 P3 B9)

13. Sodium sulphate forms a colourless, neutral solution when mixed with water.(a) Describe how this solution can be prepared in the laboratory from a named acid and

alkali. Write a chemical equation for the reaction. State symbols are not required.(b) Sodium sulphate crystals have the formula Na2S04.lOH20.Calculate

(i) the relative molecular mass of sodium sulphate crystals,(ii) the percentage by mass of water in the crystals.[Relative atomic masses AT: H, 1; 0, 16; Na, 23; S, 32] (N2003 P3 BID)

14. (a) Give three properties of all acid solutions.(b) Calcium hydroxide, a base, will react with ammonium sulphate to liberate ammoniagas. The unbalanced chemical equation for this reaction is:

Ca(OH)2 + (NH4)2S04 ~ CaS04 + NH3 + H20(i) Copy and balance this chemical equation.(ii) Calculate the relative molecular mass of anunonium sulphate. Use this relative

molecular mass to determine the mass and volume of ammonia, at roomtemperature and pressure, that will be produced when 264 g of ammoniumsulphate react with calcium hydroxide.[Relative atomic masses: A ,: H, 1; N, 14; 0, 16; S, 32J (N2004 P3 Bl1)


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SectionB1. (a) (i) Sodiumhydroxide (ii) Hydroxide ions OH-(b) (i) KOH+NH Cl ~ KCl +NH . '4 heat 3 +H20 sohd or aqueous, heat

~ ~ ) C2KloH+CuS04 ~ CU(OH)2+~S04 aqueous solutions111 0ourless(iv) Add aqueous HaCI fi 11 db He .2 0 ovve y L"W"luteprecipitate is fOrIIled.(c) Sim ilarity : Both react with acid to form salt and water.

Difference: Alkali is soluble in water; base may not be so.(d) On a dd in g a dilute acid, effervescence will be observed in potassium carbonate.

2. (a) A few drops ofmetbyl orange indicator is added to sodium hydroxide solution in a conicalflask. From a burette, hydrochloric acid is added until the indicator colour turns pink.NaOH +HCI----7NaCl +Hp

(b) pH scale is a measure of how acidic Of alkaline a solution is. pH scale runs from 1(strongly acidic) to 14 (strongly alkaline). pH 7 corresponds to a neutral solution.

(c) (i) Violetcolouration(ii) Dirty green precipitate(iii) White precipitate, soluble in excess ofNaOH. Iron(II) hydroxide

3. (a) A base that is soluble in water. It forms OR- ions in water. Itneutralizes acid to formsalt and water.

(b) (i) Turns violet(ii) White precipitate, dissolves when more CO2 is bubbled through.(e) (i) Blue flame. White ash with black soot. 2Mg + CO2 ----7MgO + C(ii) Acid is added to dissolve the MgO. On filtering, carbon is the residue.(iii) 06 g

4. (a) Solution turns blue. Bubbles/effervescence observed when copper(lI) carbonatedissolves in the acid. No more bubbles/effervescence

(b) A solution that contains the maximum amount of solute that can dissolve in it. Put acrystal of coppersulphate in the solution. The crystal remains undissolved.

(c) Water is squirted from a wash-bottle to the crystals in the filter funnel. The crystais arethen dried by being pressed between pieces of dry filter paper.

(d) Make a solution from some of the crystals. On addition of aqueous barium nitrate, awhiteprecipitate is formed,

(e) 125 g. There were impurities in the copper(Il) carbonate used.(f) Water of crystallisation is driven off by heat.5. (a) Colour change of indicator paper, egoblue litmus turns red. On adding a piece of fairly

reactive metal, eg., Mg, effervescence of hydrogen gas is seen. On adding a metalcarbonate, effervescence of carbon dioxide is seen. Reacts with a base, eg., CaO isinsoluble in water but it will dissolve inan acid.

(b) (i) Excess copper(I1) oxide is added to the dilute sulphuric acid A titration is performedwith sodium hydroxide and sulphuric acid.

(ii) CuO(s) + H2SOlaq) ----7CuS04(aq) + Rp(1) or2NaOH(aq) + H2S04(aq) -4N~SOiaq) + 2~O(1)6. (a) Colour change of indicator paper, eg., red litmus turns blue. Neutralizes acid When

heated with an ammonium salt, ammonia gas is evolved. NaOH +NH4CI----7NH} +NaCI+Hp(b) Copper(m hydroxide 2NaOH(aq) + CuSOiaq) ----7Cu(OHMs) + NazS04

7. Acids react with some metals to produce salt and hydrogen gas. Acids react with carbonatesto produce salt, carbon dioxide and water. Acids react with metal oxides and hydroxides toproduce salt and water ego H2S04(aq) + CuO(s) ----7CuS04(aq) + HP(l)


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The experiment is repeated. 25.0 ern' of sulphuric acid is placed in a conical flask, butno indicator is added. The sodium hydroxide is placed in a burette and the same volumeof this alkali is added to the flask as before. The flask will now contain a solution ofsodium sulphate without excess acid or alkali.

H2S04 + 2NaOH ~ NaZS04 + 2HzO(b) (i) M, of Na2S04.lOHp =322(ii) % by mass of water in the crystals =55.9%.14. (a) Acid solutions

- react with fairly reactive metals to produce hydrogen gas.- react with metal carbonates to produce carbon dioxide gas.- react with metal oxides and metal hydroxides to form salt and water.

(b) (i) Ca(OH)2 + (NH4)ZS04 ~ CaS04 + 2NH] + 2Hp(ii) M,of (NHJ104 =132From the equation,132 g (NH4)2S04 produce 34 g NH3264 g (NHJ ZS04 produce 68 g ammonia132 g (NH4)2S04 produce 48 dm! NH3 at room temperature264 g (NH4)2S04 produce 96 dm' NH3 at room temperature


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By neutralisation. Using phenolphthalein as indicator, the amount of acid required toneutralise a measured amount of aqueous ammonia is determned. The salt is preparedwithout the indicator. The mxture isheated toevaporate off most of the water. On cooling,crystals of ammonium nitrate are formed.

9. (a) Basic oxide, egornagries iurn oxide. Amphoteric oxide, egozinc oxide(b) Sulphur dioxide reacts with water to produce acid. S02(g) +H20(l) ~ H2SOil)[sulphurous acid]Calcium oxide is an oxide of ametal and reacts with acids (neutralization reaction) toproduce salt. CaO(s) +2HCI(aq) ~ CaCI2(aq) +H20(I)Copper (II) oxide powder is added to hot dilute sulphuric acid until some no longerdissolves. The excess copper (II) oxide is filtered off. The filtrate isheated toevaporateoff most of the water. The hot saturated solution of copper (II) sulphate is allowed tocool. The crystals of copper (II) sulphate are obtained upon filtration and drying bysqueezing them between sheets of filter paper.

250Mass ofCuS04 =1000 x 20 x 160 g = 80 g

10. (a)

(b)One spatula full ofcopper(II) oxide isadded to50ern"ofdilute sulphuric acid inabeaker.The mxture iswarmed gently tospeed updissolution. When all the copper(II) oxide hasreacted, further ,9ITIounts are added until no more will dissolve. The mxture is thenfiltered to remove the unreacted copper(II) oxide.The filtrate isevaporated toabout halfits volume. This saturated filtrate isallowed tocoolfor crystallisation to take place. The crystals of copper(II) sulphate can be filtered offand dried by pressing between pieces of dry filter paper.Eg. for reaction: CuO(s) + H2SO ~ CuSO(aq) +H20(l)0/ 0 of water of crystallisation

5 x M ofH,OM, ofCSO.5H,O x 100%36.0%

12. (a) Lime is used to neutralise excess acidity in the soil.LiITIeisused totreating exhaust gases which contain air pollutants like sulphur dioxide.

(b) (i) 0= oalcium carbonateP =calcrurn oxideQ=carbon dioxideR =calcimn hydroxide

(ii) Dilute hydrochloric acid(iii) CaCO(s) -'> CaO(s) + CO2(g) orCaCO(s) + 2HCI(aq) -'> CaC~(aq) + H20(l) + CO(g) orCaO(s) + HzO(I) ~ Ca(OH),(aq)

11. (a)

(b)

CO2(g) + Ca(OH)z(aq) -'> CaCO(s) + H0(l)13. (a) To make sodium sulphate solution

Using apipette, 25.0 cm' of sulphuric acid isplaced into aconical flask. Dilute sodiumhydroxide isptaced inaburette. Afew drops ofphenolphthalein isadded into the conicalflask. The sodium hydroxide isrun frorn the burette into the flask until apink colour isformed permanently. The volume of sodium hydroxide added is recorded.

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O level Chem Revision