Question

State the evidence of chemical change that is easily detected in the following reactions
1)Reaction between sodium chloride and silver nitrate
2I) Reaction between baking soda and vinegar​

Answer 1

Explanation:

Key Concepts

Substances react chemically in characteristic ways

A set of reactions can be used to identify an unknown substance

Summary

Students will use test liquids on different known powders and observe their reactions. Then students will use these characteristic chemical changes to help them identify an unknown powder.

Objective

Students will be able to identify and control variables to develop a test to identify an unknown powder. Students will be able to explain that a substance reacts chemically in characteristic ways and that these characteristics can be used to identify an unknown substance.

Evaluation

Download the student activity sheet, and distribute one per student when specified in the activity. The activity sheet will serve as the “Evaluate” component of each 5-E lesson plan.

Safety

Be sure you and the students wear properly fitting goggles. When using a tincture of iodine, follow all warnings on the label.

Materials for the Demonstrations

Baking soda

Cornstarch

Cream of tartar

Tincture of iodine

Vinegar

Water

Universal indicator

Graduated cylinder or beaker

2 droppers

¼ teaspoon

5 clear plastic cups

3 Popsicle sticks

Materials for Each Group

Baking soda

Baking powder

Cream of tartar

Cornstarch

Water

Vinegar

Tincture of iodine

Universal indicator

10 small plastic cups

4 droppers

8 Popsicle sticks

Testing chart (laminated or covered with wax paper)

Answer 2

The evidence of chemical change that is easily detected in the following reactions can be given as:

(i) Reaction between sodium chloride and silver nitrate - White precipitate of silver chloride

(ii) Reaction between baking soda and vinegar - Effervescence of carbon dioxide

Explanation:

• When sodium chloride reacts with silver nitrate, a double displacement reaction takes place to give silver chloride and sodium nitrate.
• Silver chloride is precipitated in the reaction. It is white in colour.
• The formation of the white precipitate can be easily detected which gives evidence of chemical change.
• The reaction can be given as: $\[NaCl(aq.) + AgN{O_3}(aq.) \to AgCl \downarrow + NaN{O_3}(aq.)\]$
• When baking soda (sodium bicarbonate) reacts with vinegar (acetic acid), sodium acetate, carbon dioxide and water are formed.
• Carbon dioxide gas gives effervescence which can be easily detected. It is evidence of chemical change.
• The reaction is given as: $\[C{H_3}COOH + NaHC{O_3} \to C{H_3}COONa + C{O_2} + {H_2}O\]$