Home

Chemistry

Chemistry practicals

Testing for anions

Select Lesson

Exam Board

Select an option

Chemistry practicals

Investigating the composition of inks

Investigating distillation methods

Investigating titrations

Preparing soluble and insoluble salts

Investigating electrolysis

Investigating rates of reaction

Testing for common gases

Testing for anions

Testing for cations

Investigating desalination of water

Using resources

Ceramics, composites and polymers

Alloys and rusting

Finite and renewable resources

Reducing the use of resources

Life cycle assessments

Potable water, treatment and purification

The Haber process

Common fertilisers and their importance

Chemistry of the atmosphere

Evolution of the Earth's atmosphere

Greenhouse gases and climate change

Combustion and pollution

Chemical analysis

Substance types and determining purity

Chromatography: phases and calculations

Flame emission spectroscopy

Organic chemistry

Hydrocarbons and crude oil

Cracking

Hydrocarbons: alkanes and alkenes

Polymers

Polyesters: types and formation - Higher

Alcohols and carboxylic acids

Rates of reaction and equilibria

Calculating rates of reactions

Catalysts

Reversible reactions and equilibria

Position of equilibrium - Higher

Energy changes

Endothermic and exothermic reactions

Energy changes in reactions

Bond energy calculations - Higher

Chemical and fuel cells

Chemical changes

Acids, bases and pH

Strong and weak acids - Higher

Reactions of acids

Titration calculations - Higher

The reactivity series of metals

Electrolysis

Extracting metals

Oxidation and reduction: redox reactions - Higher

Quantitative chemistry

Calculating relative masses

Mole calculations and Avogadro's constant - Higher

Conservation of mass

Chemical equations

Limiting reactants and masses - Higher

Concentrations of solutions

Calculating gas volumes using moles - Higher

Percentage yield and atom economy

Bonding, structure and properties of matter

Ions and their formation

Ionic bonding: properties of compounds and naming

Covalent bonding

Giant covalent substances

Metallic bonding and alloys

Changes of state

Nanoparticles: uses and hazards

Atomic structure and the periodic table

The atom and isotopes

Elements and compounds

Filtration and crystallisation

The history of the atom

Electronic configuration

The history of the periodic table

The properties of transition metals

Group 1: properties and reactivity

Group 7: properties and reactions

Group 0: properties and reactivity

Practical skills

Measuring techniques

Safety and ethics

Designing experiments

Methods of heating substances

Working with electronics

Random sampling and sampling methods

Comparing results using percentage change

Working scientifically

The scientific method

Science communication and ethics

Evaluating risks and hazards

Collecting data

Processing and presenting data

Units and equations

Structuring a scientific report and drawing conclusions

Uncertainties and evaluations

Explainer Video

Tutor: Alisha

Summary

Testing for anions

In a nutshell

Simple lab tests are done to identify which anions are present in solution.

Equations

These equations will be required for your analysis.

word EQUATION	SYMBOL EQUATION
$barium \, ion + sulfate \space ion \rightarrow \, barium \space sulfate$	$Ba^{2+}{(aq)} + SO_4(aq)^{2-} \rightarrow BaSO_4(s)$
$metal \space carbonate + hydrochloric \space acid \rightarrow \, metal \space chloride + carbon \space dioxide + water$	${MCO}_3(aq) +{HCl} (aq) \rightarrow{MCl}(aq) +{CO}_2(g) + {H}_{2}{O}(l)$
$silver \space ion + chloride \space ion\rightarrow silver \space chloride\\ \ \\silver \space ion + bromide \space ion\rightarrow \,silver \space bromide\\ \ \\silver \space ion + iodide \space ion \rightarrow \, silver \space iodide$	$Ag^{+} (aq) + Cl^{-}(aq) \rightarrow AgCl(s)\\ \ \\Ag^{+}(aq) + Br^{-}(aq) \rightarrow AgBr(s)\\ \ \\Ag^{+}(aq) + I^{-}(aq) \rightarrow AgI(s)$

Equipment list

The following equipment list can be used to conduct an experiment to identify anions.

EQUIPMENT	USE
Test tubes	To carry out the tests in.
Test rack	To hold the test tubes.
Limewater	To identify whether a carbonate was present or not.
Chemical reagents See below for the list of reagents required.	To help identify the anions present.
Measuring cylinder	To measure out the reagents.
Teat pipette	To add a few drops of a reagent.
Unknown solution	To identify the anion present.

Chemical reagents

Chemical reagent	chemical symbol
$0.4 \,mol/dm^3 \space dilute \, hydrochloric \, acid$	$HCl$
$0.4 \,mol/dm^3 \space dilute \, nitric\,acid$	$HNO_3$
$0.05 \,mol/dm^3 \space silver\,nitrate$	$AgNO_3$
$0.1 \,mol/dm^3 \space dilute \, barium\,chloride$	$BaCl_2$
$Sodium \, carbonate \, solution$	$Na_2CO_3$
$Sodium \, sulfate \, solution$	$Na_2SO_4$
$Sodium \, chloride \, solution$	$NaCl$
$Sodium \, bromide \, solution$	$NaBr$
$Sodium \, iodide \, solution$	$NaI$
$Unknown \,solution$

Experiment: Identifying anions in an unknown solution

Experimental variables

The independent variable is the one you change. The dependent variable is the one which depends on what has been changed, therefore it is the one you measure. The control variable is the one which is kept constant.

Independent variable	$solution$
Dependent variable	$observation$
Control variable	$volume \, of \, solution$

Safety precautions

When performing experiments, it is very important you consider safety precautions. This is so you and others do not get hurt.

HAZARD	RISK	SAFETY MEASURE
Chemical reagents	Can cause skin irritation and burns	Avoid contact with skin. Wear suitable gloves. Wash hands immediately after use.
Glassware	If broken can cause cuts and injuries	Avoid carrying glassware with wet hands. Avoid walking around with glassware containing chemical reagents. Do not use broken glassware.

Note: As a general rule, eye protection must be worn for all chemistry related practicals.

Experiment 1: Test for carbonates

Method

This is your instructions on how to complete the test for carbonates.

Chemistry; Chemistry practicals; KS4 Year 10; Testing for anions — Always place the test tubes in a test tube rack to ensure the experiment is carried out as safely as possibly.

1.	Measure $1 \, cm^3$ of each different sodium solution into five separate test tubes. Ensure the test tubes are labelled.
2.	Pour $1 \, cm^3$ of limewater into the sixth test tube.
3.	Add $1 \, cm^3$ of dilute hydrochloric acid to each test tube containing the sodium solutions.
4.	If you see bubbles, use a teat pipette to transfer the gas to the limewater.
5.	Record your observation. *Note:* If the limewater turns cloudy, your solution contained carbonate ions.
6.	Safely discard the reagents in the test tubes and clean thoroughly.

Experiment 2: Test for sulfates

Method

This is your instructions on how to complete the test for sulfates.

1.	Measure $1 \, cm^3$ of each different sodium solution into five separate test tubes. Ensure the test tubes are labelled.
2.	Add a few drops of dilute hydrochloric acid to each test tube.
3.	Add $1 \, cm^3$ of barium chloride to each test tube.
4.	Record your observation. *Note:* If a white precipitate forms, the compound contains sulfate ions.
5.	Safely discard the reagents in the test tubes and clean thoroughly.

Experiment 3: Test for halides

Method

This is your instructions on how to complete the test for halides.

1.	Measure $1 \, cm^3$ of each different sodium solution into five different test tubes. Ensure the test tubes are labelled.
2.	Add a few drops of dilute nitric acid to each test tube.
3.	Add $1 \, cm^3$ of silver nitrate to each test tube.
4.	Record your observation. *Note:* If a white, cream or yellow precipitate forms, the solution contained halide ions.
5.	Safely discard the reagents in the test tubes and clean thoroughly.

Experiment 4: Test for unknown solution

Method

This is your instructions on how to identify the anion in your unknown solution.

1.	Repeat the tests for carbonates, sulfates and halides on the unknown salt solution.
2.	Record your observations.
3.	Use your results from the previous three tests to identify the anion present in the unknown solution.
4.	Safely discard the reagents in the test tubes and clean thoroughly.

Analysis

This is how you will use your data to be able to form conclusions.

1.	Firstly, identify the anions present in the unknown solution.
2.	Then comment on what your results show and give a reason to why you believe those particular anions are present in your solution. Include any relevant ionic equations. Use the table below to guide you.

ANION	POSITIVE RESULT	IONIC EQUATION
Sulfate	White precipitate formed	$Ba^{2+}{(aq)} + SO_4^{2-}(aq) \rightarrow BaSO_4(s)$
Carbonate	Effervescence and limewater turns cloudy	${CO}_3 ^{2-}\,(aq) + \,2H^+ \, (aq) \rightarrow{CO}_2\,(g) + {H}_{2}{O}(l)$
Chloride	White precipitate formed	$Ag^{+} \,(aq) + Cl^{-}\,(aq) \rightarrow AgCl\,(s)$
Bromide	Cream precipitate formed	$Ag^{+}\,(aq) + Br^{-}\,(aq) \rightarrow AgBr\,(s)$
Iodide	Yellow precipitate formed	$\\ Ag^{+}\,(aq) + I^{-}\,(aq) \rightarrow AgI\,(s)$

Conclusion

In your conclusion you should discuss what you observed and the reasons for your observations. Did your solution form a precipitate? If so, what colour was it? What does this tell you about the anion present? Was there any gas produced?

Evaluation

Once you have completed your experiment, you need to consider how you obtained your results. Analyse the data and observations to determine whether the qualitative findings are credible. Is there alternative methods you could use? Discuss why they were not used. Would the test be deemed more credible if there was a second observer? If you identified any anomalous results, think about why and discuss this.

Learn with Basics

Length:

Unit 1

Ionic bonding: properties of compounds and naming

Unit 2

Ions and their formation

Jump Ahead

Unit 3