Guide to Writing Good Observations in Chemistry Practical

Question 1

Adding solutions

how to record observation? (2pt)

Answer 1

(i) colour of precipitate
(i) A ……… (colour) ppt is formed.

(ii) colour change in solution
(ii) ………… (initial colour) solution turned ………… (final colour).

Question 2

Adding solutions
(i) colour of precipitate

Answer 2

(i) A ……… (colour) ppt is formed.

Question 3

Adding solutions
(ii) colour change in solution

Answer 3

(ii) ………… (initial colour) solution turned ………… (final colour).

Question 4

Heating of solid
how to record observations? (4pt)

Answer 4

(i) change in colour of solid (before and after heating)
(i) The green powder decomposes to form a black solid.

(ii) change of state
(ii) Solid Y melts to form a yellow liquid (not solution).

(iii) colour of residue on cooling (may be different when hot)
(iii) A white residue remains.

(iv) Observation for gas
(if any)
(iv) ………….. (colour) ………….. (smell) gas evolved. (Refer to Test for gas)

Question 5

Heating of Solid
(i) change in colour of solid (before and after heating)

Answer 5

(i) The green powder decomposes to form a black solid.

Question 6

Heating of Solid
(ii) change of state

Answer 6

(ii) Solid Y melts to form a yellow liquid (not solution).

Question 7

Heating of Solid
(iii) colour of residue on cooling (may be different when hot)

Answer 7

(iii) A white residue remains.

Question 8

Heating of Solid
(iv) Observation for gas
(if any)

Answer 8

(iv) ………….. (colour) ………….. (smell) gas evolved. (Refer to Test for gas)

CO2
Bubble gas into limewater, a white precipitate will form if CO2 is present

Hydrogen gas
Hold lighted splint near edge of tube, if hydrogen is present, the splint will extinguish with a ‘pop’ sound

Question 9

Test for gas - CO2

Answer 9

Bubble gas into limewater, a white precipitate will form if CO2 is present

Question 10

Test for gas - Hydrogen gas

Answer 10

Hold lighted splint near edge of tube, if hydrogen is present, the splint will extinguish with a ‘pop’ sound

Question 11

Test for gas
How to record observations? (4pt)

Answer 11

• Effervescence
• Colour of gas
• Smell of gas
• Specific test for gas

Effervescence of colourless and odourless gas is observed.
Gas extinguished a lighted splint with a ‘pop’ sound.
Gas formed white ppt when bubbled into limewater.

Question 12

Test for gas
Effervescence

Answer 12

Effervescence of colourless and odourless gas is observed. (bubbling)

Question 13

Adding solid to solutions
How to write observations (2pt)?

Answer 13

• solubility of solid in water
• colour of the solution formed

……….. (colour) solid dissolves to form a ………….. (colour) solution.
OR
……….. (colour) solid remained insoluble.

Question 14

Using Universal Indicator
How to write observation? (1pt)

Answer 14

• colour change of Universal Indicator Green Universal Indicator turns ………… (final colour).
  Inference: Mixture is acidic/neutral/alkaline

Question 15

Using Univerrsal Indicator
Color change of universal indicator
2pt

Answer 15

Green Universal Indicator turns ………… (final colour).
Inference: Mixture is acidic/neutral/alkaline

Question 16

Using litmus paper
How to write observation

Answer 16

• colour change of litmus paper

Red/blue litmus paper remained red/blue OR turned blue/red.

Red litmus paper = acidic, Blue litmus paper = alkaline, remained same colour = neutral, no effect

Question 17

When filtering a solution/suspension
How to write observation? (2pt)

Answer 17

• Colour of residue
  The residue is a ………… (colour) solid.
• Colour of filtrate
  The filtrate is a colourless solution or ………… (colour) solution.

Question 18

When filtering a solution/suspension
* Colour of residue

Answer 18

The residue is a ………… (colour) solid.

Question 19

When filtering a solution/suspension
* Colour of filtrate

Answer 19

The filtrate is a colourless solution or ………… (colour) solution.

Question 20

Reactions with Acids
2cm3 of dilute hydrochloric acid added to 2cm3 of dilute sodium hydroxide

Observation (2pt)

Answer 20

Solution remains colourless/No visible change;

Test-tube feels warm
(Deduction: Thermal energy given out)

Question 21

Reactions with Acids

2cm3 of dilute hydrochloric acid added to one magnesium ribbon

Observations (4pt)

Answer 21

Effervescence of a colourless, odourless gas is observed and;

Gas extinguished a lighted splint with a ‘pop’ sound;

The magnesium ribbon becomes smaller gradually;

Colourless solution is formed;

Question 22

Reactions with Acids

2cm3 of dilute hydrochloric acid added to calcium carbonate

Observations (4pt)

Answer 22

Effervescence of colourless and odourless gas is observed;

Gas formed white ppt when bubbled into limewater.

Colourless solution is formed;

White solid partially dissolves to form a colourless solution.

Question 23

Reactions with Acids
2cm3 of dilute hydrochloric acid added to 2cm3 of dilute sodium hydroxide

Chemical Equation + Type of reaction?

Answer 23

HCl(aq)+ NaOH(aq) –> NaCl(aq) + H2O(l)

Type of reaction: Neutralisation

NaCl is a salt hence Na+ is a cation and Cl- is an anion

Question 24

Reactions with Acids

2cm3 of dilute hydrochloric acid added to one magnesium ribbon

Deduction of gas produced

Chemical Equation + Type of reaction

Answer 24

Hydrogen

2HCl(aq)+ Mg(s) –> MgCl2(aq) + H2(g)

Type of reaction: Acid-metal reaction

MgCl2 is a salt where Mg2+ is a cation and Cl- is an anion.

Question 25

Deduction of gas produced
2cm3 of dilute hydrochloric acid added to calcium carbonate

Chemical Equation + Type of reaction

Answer 25

Carbon Dioxide

2HCl(aq)+ CaCO3(s) –> CaCl2(aq) + H2O(l) + CO2(g)

Type of reaction: Acid-carbonate reaction

CaCO3 is a salt where Ca2+ is a cation and CO32- is an anion

Question 26

What do you write when there is no reaction?

Answer 26

Note: If there is no reaction, simply record “No visible change”.

“ppt”: precipitate.