Silicate – An Overview

2 .        Sorrel is a small green plant.

(a)        The pigments in the sorrel leaf can be separated by chromatography.

(i)         Describe how chromatography can be used to separate different pigments.

(ii)        Explain what is meant by R_f value.

(b)        Sorrel plants contain a poisonous carboxylic acid X.

What can be deduced about X from each of the following three pieces of information?

(i)         When X is warmed with acidified potassium manganate (VII), the solution changes from pink to colourless.

(ii)        Aqueous bromine is not decolourised when added to a solution of X.

(iii)       A 0.1 mol/dm³ solution of X has a pH of 3 whereas a 0.1 mol/dm³ solution of hydrochloric acid has a pH of 1.

(c)        Analysis of 10.0 g of carboxylic acid X shows that it contains 2.67 g carbon, 0.220 g hydrogen and 7.11 g oxygen.

(i)         Deduce the empirical formula of X.

(ii)        The relative molecular mass of X is 90. Deduce the molecular formula of X.

3 .        Soda-lime glass is made by heating a mixture of calcium carbonate, sodium carbonate and sand in a furnace to a high temperature.

Other glasses contain compounds called silicates. The simplified structures of a silicate and sodalime glass are shown.

(a)        Describe two differences between the silicate and the soda-lime glass.

(b)        When soda-lime glass is melted, it conducts electricity. Use the information in the diagram to explain this fact.

(c)        Calcium carbonate decomposes in the furnace. Write a balanced chemical equation for the thermal decomposition of calcium carbonate. Include state symbols.

(d)        Some types of glass contain lead ions, Pb²⁺. Dishwasher powders are highly alkaline.

(i)         Which ion is responsible for alkalinity?

(ii)        When glasses containing lead ions are washed repeatedly in a dishwasher they go slightly white in colour. Suggest a chemical explanation for why the glass goes white. Write an equation for the reaction which occurs.

(e)        Calcium carbonate reacts with hydrochloric acid.

Describe how you would investigate the rate of reaction of calcium carbonate with hydrochloric acid. Give a brief description of the apparatus you would use and the measurements you would make.

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Did you answer the Secondary Chemistry Tuition Question correctly?

2.

a.i. any two of:

• chromatography paper (with bottom of paper) in solvent
• spot of mixture put (on line)
• allow solvent to move up paper/pigments are separated as they move (vertically) up the paper

1. distance spot moves ÷ distance of solvent front from base (starting) line

b.i. it/X is a reducing agent or it/X gets oxidised or potassium manganate(VII) oxidises X

1. it/X does not contain a (C=C) double bond/X is saturated

iii. it/X is a weak acid

c.i. CHO₂

1. C₂H₂O₄

3.a.

silicate	soda-lime glass
silicate has regular arrangement of atoms no ions/named ion(s)/all atoms (covalently) bonded oxygen atoms are (covalently) bonded to two silicon atoms larger spaces/an open structure	irregular arrangement calcium/sodium ions; [ALLOW: has oxygen ions] some are only bonded by one (covalent) bond a more compact structure/collapsed structure

1. Ca²⁺/Na⁺ ions can move

1. CaCO₃(s) → CaO(s) + CO₂(g)

d.i. hydroxide/OH^–

1. Pb²⁺ + 2OH^– → Pb(OH)₂

lead hydroxide formed/lead hydroxide is white/hydroxide ions react with the lead

1. gas syringe OR inverted measuring cylinder full of water attached to flask;

(gas) measured at various time intervals/take readings of clock every so often;

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