Question

Please help!

You want to do an experiment using 47Ca (half-life=4.53 days). You will need 6.00 μg of the nuclide. What mass of CaCO3 (100% enriched in 47Ca) must you order if it will take 49 hours to be delivered to you from the nuclear facility where it is prepared?

Answer 1

use this equation: \(ln[A]_t=-\dfrac{ln(2)*t}{t_{1/2}}+[A]_o\)

\([A]_o\)=initial amount of substance
t=time
\(t{1/2}\)=half-life
\([A]_t\)= is the amount of substance after t time has passed

Answer 2

Ah...How do you calculate for t 1/2?

Answer 3

It's given in the question, half-life=4.53 days

Answer 4

Oh okay! Thank you.

Answer 5

no problem, good luck!

Answer 6

Also, will the answer be for the Ca or for CaCO3?

Answer 7

Ca only

Answer 8

Ah...Do I use molar mass and convert the amount into CaCO3?

Answer 9

One more question (Sorry DX): What will be the units then?

Answer 10

we'll what you'll find with the equation above will be the mass of Ca you need.

Convert that to moles, which is the same as CaCO3, multiply those moles by the molar mass of CaCO3.

This is in the units that you started with, (from half-life) days, (from mass) \(\mu g\)

Answer 11

Okay. I'll check in once I figure out the answer and see if it's right xD

Answer 12

make sure you use the same units for t and \(t_{1/2}\), either both in hours or both in days

Answer 13

Yep, did so.

Answer 14

good stuff

Answer 15

Okay...this is a lot of steps, and now, I'm really confused. X _ X

Answer 16

lol focus on finding the mass of Ca you need initially.

Answer 17

Found it ; ~ ;

Answer 18

sweet. now, convert it to moles of Ca. The mass needs to be in grams

Answer 19

Got it.

Answer 20

now since \(n_{Ca}=n_{CaCO_3}\), multiply \(n_{Ca}\) by the molar mass of CaCO3.

you're basically using this formula \(n=\dfrac{m}{M}\)

Answer 21

n?

Answer 22

???

Answer 23

n is moles

Answer 24

Got it.....

Answer 25

good job

Answer 26

That's it?

Answer 27

The question asked for the mass of CaCO3, right?

that's the last thing you found

Answer 28

Didn't get it xP

Answer 29

Is there an easier way to do it?

Answer 30

hm no, double-check your units or post what you did i'll tell you where you went wrong.

Answer 31

I got 9.29 picograms of calcium.

Answer 32

\(\mu g =micrograms=1.0*10^{-6}g\)

Answer 33

Oops. x_x

Answer 34

maybe thats where it went sour

Answer 35

2.10416 micrograms

Answer 36

and I got 5.25016 x 10^-8 mol :3

Answer 37

hm ill check it, give me a min

Answer 38

Sure. Thanks~

Answer 39

yep, it's right. now multiply that by the molar mass of CaCO3

Answer 40

The amount of mol of Ca by the molar mass? Or do I have to keep it in g?

Answer 41

nope. the molar mass is in units of g/mol

by multiplying moles * molar mass, you eliminate the "/mol" units, and end up with units of "grams" only.

Answer 42

Gotcha.

Answer 43

Alright. I got 5.2547 x 10^-6 g

Answer 44

yep, thats it

Answer 45

Let me try the answer in my program...

Answer 46

they might want you to implement significant digits and round

Answer 47

They want me to put down a decimal, and apparently, it's still wrong x _ x

Answer 48

then it would be 5.3 x 10^-6 g

Answer 49

Still would accept more digits x - x It'd let the answer through and say it's correct :3

Answer 50

hm k, it should be right if it wants 1 decimal place

Answer 51

I'm trying a different way...Let me see if it's right x - x