Question

How many grams of calcium phosphate can be produced when 89.3 grams of calcium chloride reacts with excess sodium phosphate?

Unbalanced equation: CaCl2 + Na3PO4 → NaCl + Ca3(PO4)2

Show, or explain, all of your work along with the final answer

Answer 1

first and most important thing, balance the equation

Answer 2

Okay I'm not entirely sure on how to go about balancing, but II will give it my best
3CaCl2+Na3 2P O8-->3Na2Cl+Ca3(PO4)2 ...This is really wrong I know..

Answer 3

you notice how the formulas changed from the first one to the second? never do that

Answer 4

when you balance chemical equations, you change the coefficients in front to act as multipliers, but don't ever change the formulas themselves. It's not like regular multiplication where you distribute things.

Answer 5

the unbalanced equation had correct formulas, so start from there

Answer 6

\[CaCl_2 + Na_3PO_4 \rightarrow NaCl + Ca_3(PO_4)_2\]

Answer 7

you did the first thing right, and balanced the calciums with 3 CaCl2's

Answer 8

I am aware that my attempt in balancing this equation was a complete fail and I am ashamed to admit that I have no clue where to start when balancing .

Answer 9

we'll give it another shot

Answer 10

\[3CaCl_2 + Na_3PO_4 \rightarrow NaCl + Ca_3(PO_4)_2\]

Answer 11

see how adding the 3 in front of the CaCl2 balances the Ca, but UNbalances the Cl's?

Answer 12

yes

Answer 13

how many Cl atoms are in 3 x (CaCl2)?

Answer 14

6?

Answer 15

correct, 6

Answer 16

now look at the other side of the arrow. Which product has Cl's in it, and are there the same number as there are in the CaCl2s?

Answer 17

NaCl, and no there are not.

Answer 18

so what coefficient can you stick in front of the NaCl to make enough copies so that there are the same number of Cl's on each side?

Answer 19

the reactants have 6 Cl's, the products only have 1

Answer 20

6NaCl?

Answer 21

that's it!

Answer 22

now, fixing one thing usually unbalances something else, so how many Na's have you just created on the products side?

Answer 23

6?

Answer 24

also good

Answer 25

now find the Na's on the reactant side. Are there enough, and how can you fix it?

Answer 26

(when you balance reactions, you're always going to be swapping sides. Fix one thing, move to the other side and fix something else. Move back to the first side, fix something else, and repeat)

Answer 27

2Na3?

Answer 28

@JFraser

Answer 29

Still there?
@JFraser

Answer 30

it's not just 2Na3, it's the whole thing: \(2Na_3PO_4\)

Answer 31

okay, so far we have 3CaCl2+2Na3PO4-->6NaCl..

Answer 32

@JFraser

Answer 33

and the \(Ca3(PO_4)_2\) is the other product too, don't forget

Answer 34

I wasn't sure of that one, thanks!

Answer 35

so now that we have the chemical equation balanced (thanks for helping) how do we apply it to the question?

Answer 36

now that the equation is balanced, it shows us the molar ratio that this reaction requires. Every time that 3 CaCl2's are used, one molecule of \(Ca_3(PO_4)_2\) is made.

Answer 37

the real problem is that you're given a mass of calcium chloride, not a number of molecules, or moles.

Answer 38

do you know how to find the moles of a solid if you're given the mass?

Answer 39

somewhat

Answer 40

I'll still try

Answer 41

so you're given 89.3g of calcium chloride, but you have to convert that to moles before you can use the balanced equation

Answer 42

okay this is where I got confused the most.

Answer 43

@JFraser I might need a little more help on this part

Answer 44

i need you to hold on for about 30 minutes, it's dinnertime

Answer 45

that's fine, worth the wait you've been such great help so far.

Answer 46

if you look at the molar masses that you find on the periodic table, every element has its own mass. Calcium has a molar mass of 40g, and chlorine has a molar mass of 35.5. the molar mass of a compound is just the sum of the masses of all of the pieces that make up the compound.

Since calcium chloride is CaCl2, each unit of CaCl2 has 1 Ca and 2 Cl's, for a total molar mass of (40g + 2(35.5g) = 111g)

This 111g is the mass of one mole of CaCl2. The coefficients in a balanced reaction tell us a MOLE ratio, not a MASS ratio, so we have to compare different substances based on QUANTITY, which is moles

Answer 47

so 89.3g/111g?

Answer 48

@JFraser

Answer 49

right. that will get you moles of calcium chloride.

Now use the moles you just calculated, and the mole RATIO from the balanced equation and set up a new conversion

Answer 50

\[0.805 moles CaCl_2* \frac{1 mole Ca_3(PO_4)_2}{3mole CaCl_2}\]

Answer 51

0.805molesCaClx1moleCa(PO4)2/3moleCaCl2=0.27?

Answer 52

yes, now turn those moles of calcium phosphate into grams using the molar mass of calcium phosphate, which will be a whole lot more than the calcium chloride is

Answer 53

0.27/71=0.0038 I feel like I did something wrong
71 comes from Ca and P's masses combined and I just divided it by the 0.27 we just found.

Answer 54

@JFraser

Answer 55

the formula for calcium phosphate is \(Ca_3(PO_4)_2\), so there are 3Ca's, 2P's, and 8O's. Recalculate the molar mass

Answer 56

much clearer thank you :)

Answer 57

and you should multiply, not divide

Answer 58

\[0.27 moles Ca_3(PO_4)_2 * (\frac{ 310g Ca_3(PO_4)_2}{1 mole Ca_3(PO_4)_2}\]

Answer 59

0.27molesCa3(PO4)2 x 310gCa3(PO4)2/1moleCa3(PO4)2=83.7

Answer 60

that's it, GJ

Answer 61

That's not it, is it?

Answer 62

it is

Answer 63

Well thank you @JFraser, you're definitely great at what you do. I appreciate all the help.

Answer 64

YW. if you have the time, be sure to write a short testimonial and fan me, it helps my score

Answer 65

@Somy @KL-RC