Ksp for calcium carbonate is 5.0 × 10⁻⁹ mol² dm⁻⁶. Calculate its solubility in mol dm⁻³ and in g dm⁻³, given Mᵣ = 100.1.

s = √(5.0 × 10⁻⁹) = 7.1 × 10⁻⁵ mol dm⁻³, which is 7.1 × 10⁻⁵ × 100.1 = 7.1 × 10⁻³ g dm⁻³.

Equal volumes of 2.0 × 10⁻³ mol dm⁻³ silver nitrate and 2.0 × 10⁻³ mol dm⁻³ sodium chloride are mixed. Will silver chloride precipitate, given Ksp = 1.7 × 10⁻¹⁰ mol² dm⁻⁶?

After mixing each ion is at 1.0 × 10⁻³ mol dm⁻³, giving an ionic product of 1.0 × 10⁻⁶ mol² dm⁻⁶, which exceeds Ksp, so a precipitate forms.

What does it mean if the ionic product of a mixture is smaller than Ksp?

The solution is unsaturated, so no precipitate forms and any solid present would dissolve.

Calculate the solubility of silver chloride in 0.10 mol dm⁻³ sodium chloride, given Ksp = 1.7 × 10⁻¹⁰ mol² dm⁻⁶.

[Ag⁺] = Ksp/[Cl⁻] = 1.7 × 10⁻¹⁰/0.10 = 1.7 × 10⁻⁹ mol dm⁻³, far below the value of 1.3 × 10⁻⁵ mol dm⁻³ in pure water.

Why does adding a common ion reduce the solubility of a sparingly soluble salt?

Increasing the concentration of one ion shifts the dissolving equilibrium back towards the solid so that the product of the ion concentrations still equals Ksp.

OCR A-Level Chemistry B H433

Development of Practical Skills in Chemistry

Topic overview Planning experiments Implementing: apparatus, units and recording data Significant figures and titration calculations Graphs, gradients and drawing a conclusion Anomalous results, precision, accuracy and types of error Calculating uncertainties and improving a method Hazards, risk and control measures Recording, processing and judging data Measuring pH, mass and volume, and choosing an indicator Reflux, distillation, purification and the standard tests PAG1 to PAG6: moles, enthalpy, qualitative analysis and organic synthesis PAG7 to PAG12: electrochemistry, rates and pH

Elements of Life

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Developing Fuels

Topic overview Molar gas volume and the ideal gas equation Gas volume calculations and measuring a gas in the laboratory Bonding and shape in organic molecules Enthalpy changes: definitions and standard conditions Bond enthalpies q = mcΔT and measuring an enthalpy change in solution Burning a fuel, correcting for heat loss, and the assumptions made Hess' law and enthalpy cycles Catalysts, heterogeneous catalysis and catalyst poisons Cracking and how it is carried out The pollutants from burning fuels and their effects Catalytic converters and cutting emissions Aliphatic and aromatic compounds, functional groups and general formulae Deducing formulae and naming a branched compound Combustion of organic compounds Addition of bromine and hydrogen halides, and the test for unsaturation Hydrogenation and hydration of alkenes Addition polymerisation Electrophilic addition mechanism Displayed, shortened and skeletal formulae Chain, position and functional group isomerism Why alkenes show stereoisomerism, and the E/Z and cis/trans rules Naming and comparing the stereoisomers Sustainable fuels: benefits and risks

Elements From the Sea

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The Chemical Industry

Topic overview Rate equations, order and the rate constant Deducing the units of k and rate calculations Half-lives Continuous monitoring, quenching and the initial rates method Reading order from concentration-time and rate-concentration graphs The Arrhenius equation and what each symbol means The ln k against 1/T plot and finding the activation enthalpy Rate-determining step and mechanism Effect of conditions on the magnitude of the equilibrium constant Economic operating conditions for an industrial process Writing a Kc expression and deducing its units ICE-table calculations and measuring Kc experimentally Chemical reactions in industrial processes Nitrogen, ammonia and the ammonium ion Oxidation states of nitrogen and the tests for nitrate and ammonium Costs, benefits and risks of industrial processes

Polymers and Life

Oceans

Topic overview Solubility in aqueous and non-aqueous solvents Lattice, hydration and solution enthalpies and how they relate Measuring an enthalpy change of solution Charge density and the size of enthalpy terms Entropy: qualitative treatment Total entropy change and the condition for feasibility The limiting temperature, and why a feasible reaction may not happen Calculating the entropy change of the system The solubility product expression, its units and calculations Predicting precipitation and the common ion effect Bronsted-Lowry theory of acids and bases Strong acids and strong bases Weak acids, Ka and pKa pH of strong acids and strong bases pH of weak acids, dilution and the limits of the approximation What a buffer is and how it resists a change in pH Buffer calculations, capacity and the natural buffers How the greenhouse effect works and which gases cause it Why a molecule absorbs, concentrations in ppm, and ocean chemistry

Developing Metals

Topic overview Manganate(VII) titrations and their calculations Thiosulfate titrations, recording results and good technique Shapes of complexes and coordination number Balancing redox equations involving acid-base reactions Simple electrochemical cells Action of an electrochemical cell Standard electrode potentials and calculating E°cell Rusting and how it is prevented Transition metals: definition, oxidation states and colours d-block electron configurations of the atoms and their ions Why transition metals show variable oxidation states Ligands and complex ions Coordinate bonding and what makes a ligand Bidentate and multidentate ligands, and finding a complex's formula Reactions of Fe2+, Fe3+ and Cu2+ with hydroxide and ammonia Catalytic activity of transition metals Origin of colour in transition metal complexes Colorimetry

Colour by Design

Topic overview How dyes attach to fibres Structure of a dye molecule Fats and oils Arenes and delocalisation Representations of benzene and enthalpy of hydrogenation Tests for the common functional groups Identifying a polyfunctional molecule from a set of test results Halogenation and nitration of benzene and the electrophiles involved The nitration mechanism, sulfonation and the Friedel-Crafts reactions Diazotisation and why it is done cold Coupling reactions, azo dyes and the route from benzene Oxidising an aldehyde and the three carbonyl tests Cyanohydrin formation and its use in synthesis Using the Data Sheet reactions to plan a route Choosing between routes on yield and atom economy Nucleophilic addition mechanism Classifying organic reactions and unfamiliar mechanisms Origins of colour in organic molecules How gas-liquid chromatography separates a mixture Retention time, peak area and the limits of the technique

Chemical Literacy

Topic overview Extracting and using data and information from a scientific text Written communication and comprehension

Mathematical Skills in Chemistry

Topic overview Units, standard form and the mole in calculations Yield, atom economy and logarithmic quantities Significant figures, means and handling data Symbols, and rearranging the standard equations Substituting into rearranged equations Reading spectra and kinetics graphs Gradients, calibration lines and the Arrhenius plot Shapes and bond angles from electron pair repulsion Chiral centres, E/Z isomerism and optical activity

Oceans

Predicting precipitation and the common ion effect

2 things to know
Components 01, 02 and 03

Overview

Recall questions on comparing the ionic product with Ksp, halving concentrations on mixing, and why a common ion reduces solubility.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Numbers

Why must the concentrations be halved when equal volumes of two solutions are mixed?

Process

How does a fall in ocean pH threaten shells made of calcium carbonate?

Questions from this subtopic

Each one with the model answer underneath.

1
Ksp for calcium carbonate is 5.0 × 10⁻⁹ mol² dm⁻⁶. Calculate its solubility in mol dm⁻³ and in g dm⁻³, given Mᵣ = 100.1.
Model answer
s = √(5.0 × 10⁻⁹) = 7.1 × 10⁻⁵ mol dm⁻³, which is 7.1 × 10⁻⁵ × 100.1 = 7.1 × 10⁻³ g dm⁻³.
2
Equal volumes of 2.0 × 10⁻³ mol dm⁻³ silver nitrate and 2.0 × 10⁻³ mol dm⁻³ sodium chloride are mixed. Will silver chloride precipitate, given Ksp = 1.7 × 10⁻¹⁰ mol² dm⁻⁶?
Model answer
After mixing each ion is at 1.0 × 10⁻³ mol dm⁻³, giving an ionic product of 1.0 × 10⁻⁶ mol² dm⁻⁶, which exceeds Ksp, so a precipitate forms.
3
Why must the concentrations be halved when equal volumes of two solutions are mixed?
Model answer
Each solution is diluted into twice its original volume, so the amount of each ion is spread through double the volume.
4
What does it mean if the ionic product of a mixture is smaller than Ksp?
Model answer
The solution is unsaturated, so no precipitate forms and any solid present would dissolve.
5
Calculate the solubility of silver chloride in 0.10 mol dm⁻³ sodium chloride, given Ksp = 1.7 × 10⁻¹⁰ mol² dm⁻⁶.
Model answer
[Ag⁺] = Ksp/[Cl⁻] = 1.7 × 10⁻¹⁰/0.10 = 1.7 × 10⁻⁹ mol dm⁻³, far below the value of 1.3 × 10⁻⁵ mol dm⁻³ in pure water.
6
Why does adding a common ion reduce the solubility of a sparingly soluble salt?
Model answer
Increasing the concentration of one ion shifts the dissolving equilibrium back towards the solid so that the product of the ion concentrations still equals Ksp.

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