Practical Skills

Question 1

How do u make a volumetric solution

Answer 1

• Weigh out using a weighing boat the mass of solid needed
• Dissolve solid in a beaker using distilled water. Include washings
• Use funnel to transfer solution to a volumetric flask
• make up to mark using distilled water
• then invert to mix

Question 2

How do you carry out a titration

Answer 2

• Rinse burette and pipettes with correct solutions
• fill burette using a plastic funnel make sure there are no bubbles
• when using pipette allow to drain and touch tip to surface. Put into conical flask
• add 2 drops of indicators
• swirl solution and add from burette
• read burette to 0.5 cm3
• repeat process to get concordant results

Question 3

What are some of the sources of error in an enthalpy change experiment

Answer 3

Heat loss

Not taking into account the specific heat capacity of cup

Question 4

5 things to consider when assessing uncertainty

Answer 4

• Resolution of instrument - manufactures tolerance on instrument
• judgements made
• procedure adopted
• size of increments

Question 5

How to calculate percentage uncertainty

Answer 5

Uncertainty
————- X100
Value

Question 6

How to calculate overall apparatus uncertainty

Answer 6

Add all the percentage errors together

Question 7

What are 3 uncertainties in titre

Answer 7

Reading the burette at start of titration
Reading the burette at end of titration
Judging the end point to within one drop

Question 8

7 improvements that can be made to an investigation

Answer 8

• Repeating to get more results increases reliability
• change concentration of solution to reduce error
• change the size of pipette to reduce error
• weighing a larger mass to reduce error
• use more accurate apparatus
• improve lagging in calorimetry experiment
• control temperature

Question 9

Why repeat experiments

Answer 9

Repeating improves reliability and identifies anomalies

Question 10

Why test more than one sample

Answer 10

Samples can have a different composition and consistency

Question 11

What should you do if a substance is corrosive

Answer 11

Handle with care wash spillages off skin or wear gloves and eye protection should be worn

Question 12

What should you do if a substance is an irritant

Answer 12

Gloves and eye protection

Question 13

What should you do if a substance is flammable

Answer 13

Keep well away from flame

Question 14

What should you do if a substance is toxic

Answer 14

Wash hands after use.

Toxicity depends on dosage if possible use fum cupboard

Question 15

Define accuracy

Answer 15

A measurement result is considered accurate if judged to be close to true value

Question 16

Define calibration

Answer 16

Marking a scale on a measuring instrument

Question 17

Define data

Answer 17

Information that has been collected

Question 18

Define measurement error

Answer 18

The difference between a measured value and the true value.

Question 19

Define anomalies

Answer 19

Values in a set of results which are judged not to be part of the variation cause by random uncertainty

Question 20

Define random error

Answer 20

These cause readings to be spread about the true value due to results varying. Cannot be corrected

Question 21

Define systematic error

Answer 21

Cause reading to differ from the true value by a consistent amount each time

Question 22

Define zero error

Answer 22

Any indication the measuring systems is giving a false reading

Question 23

Define categoric variables

Answer 23

Values that are labelled

Question 24

How to test for carbonate ions

Answer 24

Add HCl
Get effervescence

CO3 2- + 2 H+ = CO2 + H2O

Question 25

Test for sulphate ions

Answer 25

Add HCl then barium chloride White precipitate SO42- + Ba2+= BaSO4

Question 26

Test for hydroxide ions

Answer 26

Add NH4 + Ammonia gas produced OH- + NH4 + = NH3 +H2O

Question 27

Halide ion tests

Answer 27

``` Add dilute nitric acid then silver nitrate Cl- white Br- cream I - yellow Then add NH3 Cl - dissolve Br - dissolve in concentrated I- turns white in concentrated ```

Question 28

Equations for Halide ions tests

Answer 28

Cl-(aq) + Ag +(aq) ----AgCl(s)

Question 29

Carbon dioxide test

Answer 29

1. Gives very weak acid | 2. Bubbling through limewater gives a white precipitate

Question 30

Sulphur dioxide gas test

Answer 30

1. Chocking smell give weakly acidic solution | 2. When gas passed through paper soaked in potassium dichromate so reduced to green blue chromium (III) ions

Question 31

Test for hydrogen sulphide ions

Answer 31

Smell of bad eggs Passed over paper soaked in less nitrate solution to give a silvery precipitate

Question 32

Hydrogen halide gas tests

Answer 32

colourless gas produce misty fumes in moist surface Gas passed over gaseous ammonia and white fumes observed

Question 33

Test for ammonia gas

Answer 33

Pungent smell Comes into contact with gaseous hydrogen chloride white fumes are observed

Question 34

Test for chlorine gas

Answer 34

A pale green gas Turns moist litmus paper first red and then white

Question 35

Test for Mg 2+ ions

Answer 35

Add dilute sodium hydroxide Will give white precipitate because is much more insoluble Mg2+ + 2OH- -- Mg(OH)2

Question 36

Testing for Ba2+ ions

Answer 36

add dilute sodium sulphate Na2SO4 Give white precipitate because more insoluble Ba2+ + SO4 2- --- BaSO4

Question 37

Test for alkene

Answer 37

Add bromine water and it will decolourise

Question 38

Test for OH alcohols

Answer 38

Warm with acidified potassium dichromate K2Cr2O7 Turns from orange to green

Question 39

Test for aldehyde | CHO

Answer 39

1. Warm with tollens reagent = a sliver mirror 2. Add fehlings solution = blue to brick red precipitate 3. Acidified K2Cr2O7 turns orange to greens

Question 40

Test for halogenalkane

Answer 40

Add HNO3 Add AgNO3 ``` Cl = white Br = cream I = yellow ```

Question 41

Test for carboxylic acid

Answer 41

Add Na2CO3 give effervescence Then litmus paper turn red