Hydrochloric acid and phenolphthalein

MOHAMMED ALNAIMI

LAB EXPERIMENT 1

OBSRVATIONS OF CHEMICAL CHANGES

PURPOSE OF EXPERIMENT

The purpose of the experiments were to observe chemical changes on various chemicals. The experiment was to distinguish between burning and heating.

PROCEDURE

A few drops of hydrochloric acid were dropped in a product labelled sodium hydrogen carbonate. Silver nitrate solution was also reacted with aqueous sodium hydroxide solution.

Magnesium metal, zinc metal, copper carbonate and copper nitrate were heated in one experiment separately and then burned.

OBSERVATIONS

When sodium hydrogen carbonate was reacted with hydrochloric acid, there was no color change. However, bubbling and fizzling occurred. The test for starch with IKI indicator resulted in a blue-black color of the solution. Reaction of potassium iodide with lead nitrate solution produced a yellow color. When phenolphthalein indicator was added to a solution of sodium hydroxide, there was a color change to bright pink. The indicator did not result in any color change when it was added to hydrochloric acid.

Reaction of silver nitrate and sodium hydroxide resulted into a light brown, black starches. Silver nitrate reacted with aqueous ammonia, and the observation was a white and cloudy solution formed. When the solution was absorbed into a paper towel and exposed to sunlight, color changed to brown and rusty. When aqueous ammonia was reacted with copper (II) sulphate, a blue solution was formed.

Reactant A

Reactant B

Observation

sodium hydrogen carbonate

hydrochloric acid

No color change

bubbling and fizzling

Starch

IKI indicator

a blue-black color

potassium iodide

lead nitrate solution

yellow color

phenolphthalein indicator

sodium hydroxide

color change to bright pink

phenolphthalein indicator

Hydrochloric acid.

No color change

silver nitrate

sodium hydroxide

light brown, black starches

Silver nitrate

aqueous ammonia

a white and cloudy solution. When the solution was absorbed into a paper towel and exposed to sunlight, color changed to brown and rusty

copper (II) sulphate

aqueous ammonia

blue solution

Magnesium metal was silver and shiny. After heating, it glowed bright red and became a white ash. Zinc metal which is rock-like and silvery melted into liquid after heating. Copper carbonate turned black upon heating while copper (II) nitrate melted and turned green, and lots of fizzing and gas were released, it finally turned black, however.

Substance

Heating

Burning

Magnesium metal

glowed bright red and became a white ash

Glowed red, then turned into a bright white flame, then turned into ash

Zinc metal

melted into liquid

Melted into a liquid, glowed red

Copper carbonate

turned black

The flame glowed blue and the powder turned black

copper (II) nitrate

Melted and turned green, and lots of fizzing and gas were released, it finally turned black, however.

The flame glowed green, and the crystals bubbled and turned black

LAB ANSWERS

Exercise 1.

1. In order to test whether a lab product contained sodium hydrogen carbonate, a few drops of hydrochloric acid would be added. If there is fizzing and bubbling of a gas, the household product is then sodium hydrogen carbonate.

2. The chemical equation for reaction between silver nitrate and sodium hydroxide is:

3. The reaction which produced the products was the one between hydrochloric acid and sodium hydrogen carbonate. There was fizzing and bubbling of gas due to production of

4. Since the sample with a faint odor turned pink, I would say that it is sodium hydroxide. Vinegar is made up to acetic acid, and phenolphthalein doesn’t cause a color change in acids.

5. The fifth cookie brand which gives a yellow-brown color does not have as much starch as compared to the other brands.

6. In order to confirm presence or absence of lead, some drops of the hair tonic would be dropped into some potassium iodide. If the solution is yellow, then there is some lead in the hair tonic.

7. Cutting a cake into 8 pieces is a physical change. This is because no new substance is formed.

8. When soda is poured into glass and the soda bubbles, it is a result of chemical change. This is because a gas is released, meaning that a certain substance in the soda has transformed.

9. In well B1, specifically in the second step, the reactant was direct sunlight. This is a chemical reaction because it turned color of dark brown similar to rust on the paper towel meaning a new substance was formed.

10. Phenolphthalein acts well as an acid/base indicator. The observation in A5 do support this statement. This is because HCl doesn’t change whereas the base turns to pink.

Exercise 2

1. The similarities of burning and heating magnesium are that there was a chemical change, resulting in the metal burning and producing ash. The difference is that when burned, magnesium burst into a bright white light while heating it made it to glow red and turn into ashes.

2. There were no differences observed in heating and burning of zinc metal. There was chemical change in burning since it only melted into a liquid.

3. Heating copper carbonate turned the powder into black and a powder was released. Burning it also resulted into formation of a black substance. There was a chemical change in both heating and burning.

4. Heating and burning copper nitrate was exactly the same. However, a glowing flame was absent when heating. There was a chemical change in burning.

5. The differences between heating and burning are that heating adds thermal energy while burning is a chemical reaction called oxidation.

6. Chemical producing a physical change was mossy zinc (it melted into liquid.

CONCLUSIONS

When two chemicals react, a product is formed and the two chemicals are said to have undergone a chemical change. This is because they have been transformed. Physical change only involves change of state. Chemicals react differently to both heating and burning. More differences are observed when heating the chemicals, however.