Unit notes and practice questions
Everything here is for unit 2 of the Grade 9 Chemistry textbook: what the chapter covers, the short notes, practice questions with their answers, and the lesson video where one exists.
The cards filed under this chapter on the Grade 9 Chemistry page. Open one at a time.
When you use it
Use whenever mixing concentrated acid with water in the laboratory.
Watch out
Always add acid to water, never water to acid. Adding water to concentrated acid causes violent heat release and dangerous spattering.
Drafted from Grade 9 Chemistry, pages 19-52, then checked twice before it went up
When you use it
Use to convert temperature values between Celsius and Kelvin scales.
Watch out
Never write a degree symbol on Kelvin temperatures. Write K, not degree K.
Drafted from Grade 9 Chemistry, pages 19-52, then checked twice before it went up
When you use it
Use to calculate the density, mass, or volume of a substance.
Watch out
Check unit consistency. Mass in grams and volume in mL or cm^3 gives g/mL or g/cm^3, not kg/m^3.
Drafted from Grade 9 Chemistry, pages 19-52, then checked twice before it went up
| Base Quantity | Name of Unit | Symbol |
|---|---|---|
| Length | Meter | |
| Mass | Kilogram | |
| Time | Second | |
| Electrical current | Ampere | |
| Temperature | Kelvin | |
| Amount of substance | Mole | |
| Luminous intensity | Candela |
When you use it
Use when identifying or expressing the seven fundamental physical measurements.
Watch out
Mass is the only SI base unit that already includes a prefix (kilo- in kilogram).
Drafted from Grade 9 Chemistry, pages 19-52, then checked twice before it went up
When you use it
Use to round calculated answers to the correct precision after arithmetic operations.
Watch out
Addition and subtraction are limited by the fewest decimal places. Multiplication and division are limited by the fewest total significant figures.
Drafted from Grade 9 Chemistry, pages 19-52, then checked twice before it went up
10 multiple-choice questions written against this chapter, each with its answer and the reason. Try one before you open the answer.
Question 1
Which of the following is the SI base unit used to measure the amount of a substance?
Answer: B Mole
Why
According to the SI base units table, the mole (mol) is the base unit for the amount of substance. Kilogram measures mass, candela measures luminous intensity, and ampere measures electrical current.
Question 2
According to laboratory safety rules, what is the correct way to mix acid and water?
Answer: B Always pour acid into water
Why
Always pour acid into water. Pouring water into acid can cause the acid to spatter violently out of the container.
Question 3
What is the first step in the scientific method?
Answer: B Observation and formulation of a question
Why
The scientific method begins with observation and formulation of a question about a phenomenon in the natural world.
Question 4
In chemistry laboratory work, one liter (1 L) is equal to which of the following volumes?
Answer: B 1 dm3
Why
A liter is a unit of volume equal to 1 cubic decimeter (1 dm3), which also equals 1000 cm3 or 1000 mL.
Question 5
How many significant figures are in the measurement 0.00420 min?
Answer: B 3
Why
Zeros to the left of the first nonzero digit are not significant. The trailing zero to the right of the decimal point is significant. Therefore, only the digits 4, 2, and the last 0 are significant (3 significant figures).
Question 6
Based on standard SI metric prefixes, how many meters are in 1 Megameter (Mm)?
Answer: B 1 x 106 m
Why
The prefix Mega (M) represents a multiplying factor of 106 (1,000,000). Thus, 1 Mm = 1 x 106 m.
Question 7
A temperature reading in Adama is 25.00 °C. What is this temperature on the Kelvin scale?
Answer: B 298.15 K
Why
The relationship between Celsius and Kelvin is K = °C + 273.15. Substituting 25.00 gives 25.00 + 273.15 = 298.15 K.
Question 8
A student repeats a mass measurement three times and gets values that are very close to one another, but all three values are far from the true mass. These measurements are:
Answer: A Precise but not accurate
Why
Precision refers to the closeness of repeated measurements to each other. Accuracy refers to closeness to the true value. Getting reproducible values far from the true value means the data is precise but not accurate.
Question 9
Chaltu measured a 35.1 mL sample of an unknown solvent in the laboratory and found its mass to be 30.5 g. What is the density of this liquid?
Answer: A 0.869 g/mL
Why
Density is mass divided by volume: d = m / V. Dividing 30.5 g by 35.1 mL gives 0.869 g/mL.
Question 10
A student adds two mass readings: 89.332 g + 1.1 g. According to the rules of significant figures for addition, what is the correct result?
Answer: C 90.4 g
Why
In addition and subtraction, the result cannot have more decimal places than the starting measurement with the fewest decimal places. Because 1.1 g has only one decimal place, the sum 90.432 g is rounded to 90.4 g.
The app holds 12 questions on this unit, marked as you go. These are the first 10.
Unit 2 runs from page 19 to page 52 of the Ministry of Education edition.
Ministry of Education edition, English, 186 pages
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