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chemistry alevel

7 How many neutrons are present in 1.0g of helium?
[Avogadro]
(1)
A 3.0 × 1023
B 1.5 × 1023
C 1.0 × 1023
D 0.5 × 102

how c i keep getting b

Reply 1

staerryynighht

7 How many neutrons are present in 1.0g of helium?
[Avogadro]
(1)
A 3.0 × 1023
B 1.5 × 1023
C 1.0 × 1023
D 0.5 × 102

how A I KEEP GETTING B

Reply 2

PizzaMan2989

how many moles of He do u have? multiply that by Avogadro's constant

Reply 3

PizzaMan2989

wait that gives B as well

(edited 3 years ago)

Reply 4

PizzaMan2989

oh ok. The 1.505 tells u the number of atoms. there are two neutrons for every atom hence 3x10^23

Reply 5

staerryynighht

Original post by PizzaMan2989

oh ok. The 1.505 tells u the number of atoms. there are two neutrons for every atom hence 3x10^23

thanks ! can you do A hydrocarbon contains, by mass, 80% carbon and 20% hydrogen.
The molecular formula for the hydrocarbon is
(1)
A CH3
B C2H5
C C2H6
D C4H10

as well tysm

Reply 6

PizzaMan2989

A?
n(C) = 80/12 = 6.6
n(H) = 20/1 = 20

divide by lowest no. so 6.6
ratio is therefore 1 to roughly 3, CH3

Reply 7

PizzaMan2989

and nw 😁. what other a levels do u take?

Reply 8

charco

Study Forum Helper

Original post by staerryynighht

7 How many neutrons are present in 1.0g of helium?
[Avogadro]
(1)
A 3.0 × 1023
B 1.5 × 1023
C 1.0 × 1023
D 0.5 × 102

how c i keep getting b

1g = 0.25 mol He
1 mol He contains 2 mol neutrons
0.25 mol contains 0.25 x 2 = 0.5 mol neutrons
1 mol = 6 x 10²³
0.5 mol = 0 3 x 10²³ neutrons
Answer A