Question

density & chemical changes 6th grade review
this is what i should have learned during this unit:
i can identify the formation of a new substance by using the evidence of a possible chemical change such as production of a gas, change in temperature, production of a precipitate, or color change.

• i can calculate the density of substances.

1. the image shows what happens when cold medicine tablets are placed in room temperature water. image: glass with tablets, labels: bubbles produced, water level rises, tablets dissolve, water becomes cloudy

what evidence would indicate that a chemical change has occurred?
a. the tablets dissolved in water.
b. the water becomes cloudy.
c. the water level increases slightly.
d. bubbles are given off and there is a temperature change.

1. four mixtures are made by combining two clear liquids, and observations are made. which mixture demonstrates a chemical change has occurred?

a. mixture 1: the combined liquids have a greater mass than either of the starting liquids.
b. mixture 2: the liquids, when mixed, produced a solid which settled to the bottom.
c. mixture 3: the mixture of the two liquids takes the shape of the container.
d. mixture 4: the denser of the two liquids lies below the other, less dense liquid.

1. a student needs to find the density of a cube. the height of the cube is 4 cm³ (likely 4 cm) and the mass of the cube is 192 g. what is the approximate density of the cube?

a. 0.4 g/cm³
b. 3.0 g/cm³
c. 4.0 g/cm³
d. 0.3 g/cm³

Explanation:

Question 1

• Option A: Dissolving is often physical (solvation, no new substance).
• Option B: Cloudiness could be suspension (physical).
• Option C: Volume change is physical (displacement).
• Option D: Bubbles (gas production) and temp change are chemical change indicators (new substance formed).

• Option A: Mass conservation (physical, no new substance).
• Option B: Precipitate (solid from liquids) is a chemical change (new substance).
• Option C: Taking container shape is physical (liquid property).
• Option D: Density - based layering is physical (no reaction).

Step1: Find volume of cube.

A cube has side length \( s = 4\space cm \) (note: unit should be \( cm \), not \( cm^3 \)). Volume \( V = s^3 = 4^3 = 64\space cm^3 \).

Step2: Calculate density.

Density formula: \(
ho=\frac{m}{V} \), where \( m = 192\space g \), \( V = 64\space cm^3 \). So \(
ho=\frac{192}{64}=3.0\space g/cm^3 \).

Answer:

D. Bubbles are given off and there is a temperature change.

Question 2