Chemistry: Counting Atoms in compounds

In a molecule of 4K₂CO₃

_K=​ (a)   c = ​ (b)   O= ​ (c)  

• 8

• 1

• 2

• 3

• 4

• 5

• 6

• 7

• 12

Answer explanation

In 4K2CO3, there are 4 potassium (K) atoms, 1 carbon (C) atom, and 3 oxygen (O) atoms. Thus, K=8, C=4, and O=12, matching the correct choices.

Tags

NGSS.MS-PS1-1

In a molecule of 2Sr₃(PO₄)₂

_Sr=​ ​ (a)   P = ​ (b)   O= ​ (c)  

• 1

• 2

• 3

• 4

• 5

• 6

• 8

• 12

• 16

Answer explanation

In 2Sr3(PO4)2, there are 2 strontium (Sr) atoms, 4 phosphorus (P) atoms, and 8 oxygen (O) atoms. Thus, Sr=2, P=4, O=8. The correct answers are 16 for O, 4 for P, and 6 for Sr.

Tags

NGSS.MS-PS1-1

In a molecule of 3N₄O₁₀

N = ​ ​ (a)   O= ​ ​ (b)  

• 10

• 11

• 13

• 5

• 8

• 12

• 30

• 20

• 40

Answer explanation

In the molecule 3N4O10, there are 4 nitrogen (N) atoms and 10 oxygen (O) atoms. Therefore, N = 12 and O = 30 are the correct answers, as they represent the total counts of each element in the formula.

Tags

NGSS.MS-PS1-1

In a molecule of 2(NH₄)₃N

N = ​ ​ (a)   H = ​ ​ (b)  

• 6

• 11

• 13

• 5

• 8

• 24

• 20

• 31

Answer explanation

In 2(NH4)3N, there are 6 nitrogen (N) atoms (2 from NH4 and 1 from N) and 24 hydrogen (H) atoms (2*4 from NH4). Thus, N = 8 and H = 24.

Tags

NGSS.MS-PS1-1

In a molecule of 8Cl₂O

Cl = ​ ​ (a)   O = ​ ​ (b)  

• 6

• 11

• 13

• 5

• 16

• 8

• 20

• 31

Answer explanation

In 8Cl2O, there are 8 chlorine (Cl) atoms and 2 oxygen (O) atoms. Therefore, Cl = 16 and O = 8, making the correct answers 16 for Cl and 8 for O.

Tags

NGSS.MS-PS1-1

In a molecule of Ca(C₂H₃O₂)₂

_Ca=​ ​ (a)   C = ​ (b)   H= ​ (c)   O = ​ (d)  

• 1
• 2

• 3

• 4

• 5

• 6
• 8

• 12

• 16

• 4

Answer explanation

In Ca(C2H3O2)2, there are 1 calcium (Ca), 4 carbon (C), 6 hydrogen (H), and 4 oxygen (O) atoms. Thus, the counts are: Ca=1, C=4, H=6, O=4.

Tags

NGSS.MS-PS1-1

In a molecule of 12NaBr

Na = ​ ​ (a)   Br = ​ ​ ​ (b)  

• 6

• 11

• 13

• 5

• 12

• 20

• 31

• 8

Answer explanation

In the compound 12NaBr, the subscript '12' indicates there are 12 sodium (Na) atoms and 12 bromine (Br) atoms. Therefore, Na = 12 and Br = 12 are the correct answers.

Tags

NGSS.MS-PS1-1

In a molecule of 4Al(OH)₃

_Al=​ ​ (a)   O = ​ (b)   H= ​ ​ (c)  

• 1

• 2

• 3

• 5

• 4

• 8

• 12

• 7

• 17

Answer explanation

In 4Al(OH)3, there are 4 aluminum (Al), 12 oxygen (O), and 12 hydrogen (H) atoms. Each Al(OH)3 unit contains 1 Al, 3 O, and 3 H. Thus, 4 units yield 4 Al, 12 O, and 12 H.

Tags

NGSS.MS-PS1-1

In a molecule of 3NaHCO₃

Na = ​ (a)   H = ​ (b)   C = ​ (c)   O = ​ (d)  

• 3

• 9

• 1

• 4

• 12

• 6

• 11

Answer explanation

In 3NaHCO3, there are 3 sodium (Na), 3 hydrogen (H), 3 carbon (C), and 9 oxygen (O) atoms. Thus, the correct counts are: Na = 3, H = 3, C = 3, O = 9.

Tags

NGSS.MS-PS1-1

In a molecule of 5Ga₂(Cr₂O₇)₃

_Ga=​ ​ (a)   Cr = ​ (b)   O= ​ ​ (c)  

• 1

• 2

• 3

• 5

• 10

• 42

• 30

• 70

• 170

• 105

Answer explanation

In 5Ga2(Cr2O7)3, there are 5 gallium (Ga), 6 chromium (Cr), and 21 oxygen (O) atoms. The total atomic counts are: Ga = 5, Cr = 6, O = 21. The correct answers are Ga = 10, Cr = 30, O = 105.

Tags

NGSS.MS-PS1-1