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IGCSE Chemistry Extended12.5.3—Gas tests: NH3 with damp red litmusTopic Practice

12.5.3—Gas tests: NH3 with damp red litmus

• Describe gas tests: NH3 with damp red litmus; CO2 with limewater; Cl2 with damp litmus; H2 with lighted splint; O2 with glowing splint; SO2 with acidified aqueous potassium manganate(VII)

Question 1(e)

[Maximum number: 1]

The following formulae represent different substances.
A
Ag
CaCO3\mathrm{CaCO}_{3}CH4\mathrm{CH}_{4}Cl2\mathrm{Cl}_{2}
Cu
SO2\mathrm{SO}_{2}

Answer the following questions using only these substances.
Each substance may be used once, more than once or not at all.
State which substance is:

a gas which bleaches damp litmus paper

Question 1(g)

[Maximum number: 1]

Diamond and graphite are different solid forms of carbon. The carbon atoms in diamond and graphite are arranged in different ways.

All forms of carbon burn to produce carbon dioxide.

Name the substance used to test for carbon dioxide.

Question 1(a)(iii)

[Maximum number: 1]

This question is about gases.

The following substances are gases at room temperature.

Table

Identify, by letter:

a gas which bleaches damp litmus paper [1]

Question 1(c)

[Maximum number: 1]

The names of nine substances are shown.
> aluminium oxide ammonia carbon monoxide anhydrous cobalt(II) chloride hydrated copper(II) sulfate iron(III) oxide nitrogen dioxide silver steel

Answer the following questions using these substances. Each substance may be used once, more than once or not at all.

Name the substance that is:

an alkaline gas ..... [1]

Question 2(b)(iii)

[Maximum number: 2]

Magnesium exists as three isotopes, 1224Mg,1225Mg{ }_{12}^{24} \mathrm{Mg},{ }_{12}^{25} \mathrm{Mg} and 1226Mg{ }_{12}^{26} \mathrm{Mg}.

All isotopes of magnesium react with dilute hydrochloric acid to make hydrogen and a salt.

Describe a test for hydrogen.
test
result

Question 2(c)(i)

[Maximum number: 1]

Calcium hydroxide, Ca(OH)2\mathrm{Ca}(\mathrm{OH})_{2}, is slightly soluble in water.

Limewater is a saturated solution of calcium hydroxide, Ca(OH)2(aq)\mathrm{Ca}(\mathrm{OH})_{2}(\mathrm{aq}).

Name the gas limewater is used to test for.

Question 2(d)(ii)

[Maximum number: 2]

Sulfur dioxide is a toxic gas.

Describe the test for sulfur dioxide.
test
observations

Question 2(b)(i)

[Maximum number: 1]

Lithium, sodium and potassium are Group I elements.

Sodium reacts with cold water to form hydrogen gas and a solution of a strong alkali.

State the test for hydrogen gas.
test
positive result

Question 2(c)

[Maximum number: 2]

Silver dichromate, Ag2Cr2O7\mathrm{Ag}_{2} \mathrm{Cr}_{2} \mathrm{O}_{7}, is a red insoluble salt.
Silver dichromate can be made by reacting silver nitrate solution with ammonium dichromate solution. The chemical equation for the reaction is shown.

2AgNO3(aq)+(NH4)2Cr2O7(aq)→2NH4NO3(aq)+Ag2Cr2O7( s)2 \mathrm{AgNO}_{3}(\mathrm{aq})+\left(\mathrm{NH}_{4}\right)_{2} \mathrm{Cr}_{2} \mathrm{O}_{7}(\mathrm{aq}) \rightarrow 2 \mathrm{NH}_{4} \mathrm{NO}_{3}(\mathrm{aq})+\mathrm{Ag}_{2} \mathrm{Cr}_{2} \mathrm{O}_{7}(\mathrm{~s})

Dilute aqueous sodium hydroxide was added to the ammonium nitrate solution made in the reaction. The mixture was then warmed and damp Universal Indicator paper was held above the mixture.

State and explain what would happen to the Universal Indicator paper.

Question 3(f)(i)

[Maximum number: 2]

Tin is a metallic element in Group IV. Its main ore is cassiterite which is an impure form of tin(IV) oxide, SnO2\mathrm{SnO}_{2}.
Tin also occurs in stannite, Cu2FeSnS4\mathrm{Cu}_{2} \mathrm{FeSnS}_{4}.

Copper(II) nitrate, Cu(NO3)2\mathrm{Cu}\left(\mathrm{NO}_{3}\right)_{2}, decomposes when it is heated. The only solid product is copper(II) oxide, CuO . There are two gaseous products. One of the gaseous products is oxygen.

Describe a test for oxygen.
test
result

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