Chemistry-Unit 2 Review

SI units& density

100

What is the SI unit used to measure the amount of something?

mole (mol)

200

What are the 2 SI units for temperature?

K  and  ^oC

300

What are the 2 commonly used units (unit symbols) for density?

g/mL  and  g/cm³

400

What is the volume of an object that has a density of 2.7 g/mL and a mass of 6.0 grams?
(You MUST include the proper units on your answer.)

2.2 mL

500

What is the density of a metal that has a mass of 5.7 grams and a volume of 11.2 cm³?  
(You MUST include units on your answer!)
**BONUS 500 points for correct rounding & Sig Figs!

0.51 g/cm³

ConvertingUnits

100

ML (not mL) is the symbol for which unit?

megaliter

200

How many micrograms is in 1 gram?

1,000,000 micrograms = 1 gram

300

Using the dimensional domino method, convert 1234 centimeters to meters.
You MUST show your work and label your answer with the correct unit.

1234 cm  |    1 m       =  12.34 m
              |  100 cm

400

Using the dimensional domino method, convert 256 m to km.
You MUST show your work and label your answer with the correct unit.

256 m  |  1 km      =  0.256 km
           |1000 m

500

Using the dimensional domino method, convert 120,000 micromoles to kilomoles.
You MUST show your work and label your answer with the correct unit.
**BONUS 500 points for using correct Sig Figs!

120,000 𝜇mol  |      1 mol           |  1 kmol    =
                      | 1,000,000 𝜇mol | 1000 mol

0.00012 kmol  or 1.2 x 10^-4 kmol

ScientificNotation

100

In scientific notation, the coefficient needs to be between which 2 numbers.

between 1 and 10

200

In scientific notation we use an exponent on the 10. When should this exponent be positive AND when should the exponent be negative?

POSITIVE exponents are used for big numbers.
NEGATIVE exponents are used for small numbers.

300

Express the number 6.57 x 10⁶ in expanded/standard form.

6.57 x 10⁶ (positive exponent = big number)
6. 5 7 0 0 0 0     6,570,000
   U U U U U U
   1 2  3 4 5 6

400

Express the number 5.20 x 10^-3 in expanded/standard form.
**BONUS 100 points for using correct Sig Figs!

     5.20 x 10^-3 (negative exponent = small number)
0 0 5. 2 0      0.00520   (3 sig figs)
U U U 
3 2  1

500

Express the number 0.0007420 in scientific notation.
**BONUS 500 points for using correct Sig Figs!

0.0007420  =    7.420 x 10^-4 (neg. exp., 4 sig figs)
  UUUU
  1234

SigFigs

100

How many sig figs are in the number 2021

2 0 2 1 
(all 4 are significant, trapped zero)

200

How many sig figs are in the number 2020

2 0 2 0
(3 sig figs. Zero at the end is a placeholder.)

300

How many sig figs are in the number 0.0024010

0.0 0 2 4 0 1 0 
(5 sig figs.Trapped zero and zero after the decimal are significant. Leading zeros are placeholders.)

400

Perform the following calculation. Use correct sig figs AND rounding on your answer. 

853.2 - 627.433 = ?

853.2 - 627.433 = ?
 1 dec.        3 dec.

calculator answer: 225.767

rounded answer: 225.8 
(1 decimal, round up when the next number is ≥6)

500

!! DAILY DOUBLE !!

Perform the following calculation. Use correct sig figs AND rounding on your answer. 

81.06 x 0.020 x 188.74 = ?

HINT: You may need to write your answer in scientific notation.

81.06 x 0.020 x 188.74 = ?
   4          2           5

calculator answer: 305.985288

rounded answer: 300 (2 sig figs, drop digits ≤5)
(write as 3.0 x 10² for 2 sig figs)

Accuracy, Precision,% Error

100

A sample of metal is known to have a volume of 123.45 cm³. Two lab groups measured the volume of the metal; they're findings are shown below.

	Student 1	Student 2	Student 3
Group 1	123.40	123.55	122.90
Group 2	120.12	120.15	120.20

Which Group had more ACCURATE measurements?

	Student 1	Student 2	Student 3
Group 1	123.40	123.55	122.90
Group 2	120.12	120.15	120.20

Group 1 had more accurate measurements because they were closest to the known value of 123.45 cm³

200

The density of a liquid is known to be 2.50 g/mL. Two lab groups measured the liquid's mass and volume to calculate the density; they're results are shown below:

	Student 1	Student 2	Student 3
Group 1	2.55	2.60	2.40
Group 2	2.12	2.10	2.15

Which group had the more PRECISE measurements?

	Student 1	Student 2	Student 3
Group 1	2.55	2.60	2.40
Group 2	2.12	2.10	2.15

Group 2 was more precise because the densities were closer together than the measurements in Group 1.

300

In a lab, a student recovered 3.60 grams of a solid. The expected amount was 3.45 grams. Calculate this student's percent error.

SHOW YOUR WORK & round your answer to the tenths.

(3.60 - 3.45)   x 100  =  4.3% error
       3.45

400

	Trial 1	Trial 2	Trial 3
Group 1	2.55	2.60	2.40
Group 2	2.12	2.10	2.15

What is the percent error for Group 2's Trial 2 if the expected value was 2.05 ?

SHOW YOUR WORK & round your answer to the hundredths.

(2.10 - 2.05)   x 100  =  2.44% error
       2.05

500

	Trial 1	Trial 2	Trial 3
Group 1	2.55	2.60	2.40
Group 2	2.12	2.10	2.15

What is the percent error for Group 1's Trial 2 if the expected value was 2.83 ?

SHOW YOUR WORK & round your answer to the hundredths.

(2.60 - 2.83)   x 100  =  —8.13% error
       2.83