[charlie1983]

Hello, I am using a workbook to practice and there have been a few times that the answer in book differs from mine and I can't find an explanation for the difference in answers. Sometimes the book's answer is given in scientific notation and, other times it isn't. Is there a rule for the use of scientific notiation that I am missing?

Please bear with me, here are 2 problems:

#1 Equation: Ca(OH)2 + 2NH4CL---->CaCL2 + 2H2O + 2NH3
How many grams of calcium chloride can be produced along with 60.2 grams of ammonia?

My answer is 196 g CaCL2, the book's answer is 202 g CaCL2; Can you explain please?

Problem #2

Equation: NaCL + NH4HCO3 ---->NaHCO3 + NH4CL
How much NaCL is needed to react completely with 83.0 grams of NH4HCO3?

My answer is 6.14 x 10^1; The book's answer is 61.4 g NaCL; I don't understand... Thanks

[Albert]

#1 Equation: Ca(OH)2 + 2NH4CL---->CaCL2 + 2H2O + 2NH3
How many grams of calcium chloride can be produced along with 60.2 grams of ammonia?

My answer is 196 g CaCL2, the book's answer is 202 g CaCL2; Can you explain please?

I got 196g too. It's just a matter of what atomic mass the author(s) used.

Problem #2

Equation: NaCL + NH4HCO3 ---->NaHCO3 + NH4CL
How much NaCL is needed to react completely with 83.0 grams of NH4HCO3?

My answer is 6.14 x 10^1; The book's answer is 61.4 g NaCL; I don't understand... Thanks

What's the difference between 6.14 x 10^1 and 61.4?

[Borek]

Sometimes the book's answer is given in scientific notation and, other times it isn't. Is there a rule for the use of scientific notiation that I am missing?

No hard rules here that I am aware off.

#1 Equation: Ca(OH)2 + 2NH4CL---->CaCL2 + 2H2O + 2NH3
How many grams of calcium chloride can be produced along with 60.2 grams of ammonia?

My answer is 196 g CaCL2, the book's answer is 202 g CaCL2; Can you explain please?

Book is wrong. Exact answer is 196g.

Equation: NaCL + NH4HCO3 ---->NaHCO3 + NH4CL
How much NaCL is needed to react completely with 83.0 grams of NH4HCO3?

My answer is 6.14 x 10^1; The book's answer is 61.4 g NaCL; I don't understand... Thanks

6.14*10 and 61.4 are the same number. As I have already told you there is no general "hard" rule describing when to use which notation. In most cases that's the matter of style and aesthetics.

2 comments:

Chlorine is Cl, not CL

Try to use EBAS (see my signature) whenever you have doubts about the result of stoichiometric calculations.

[Borek]

I got 196g too. It's just a matter of what atomic mass the author(s) used.

That was my first idea too, but it seems unlikely. For 202 answer CaCl₂ molar mass must be calculated as 114.4. No way of making such huge error just because of different molar massses used.

Heh, did some number twiddling Check what is the answer for 62.0g of ammonia, not 60.2g

[Albert]

Heh, did some number twiddling Check what is the answer for 62.0g of ammonia, not 60.2g

Funny! The authors were drinking, I guess. 

[sdekivit]

as for scientific numbers: most of the time they are used to become a right amount of significant numbers.

For problem 2 the least amount of significant numbers in the question is 3 (83.0) so both 61.4 as 6.14 x 10^1 are both correct.

But when for example 2.0 mol gas has a pressure of 134535,67 Pa then it's useful to use scientific notation: 1.3 x 10^5 Pa.

[Borek]

as for scientific numbers: most of the time they are used to become a right amount of significant numbers.

What are scientific numbers? Numbers written using scientific notation?

I guess you mean "scientific notation is used to clearly show correct number of significant digits". As in 6.13*10⁶ instead of 6130000.

But when for example 2.0 mol gas has a pressure of 134535,67 Pa then it's useful to use scientific notation: 1.3 x 10^5 Pa.

It depends on how precisely pressure was measured. If the pressure was measured with 8 SD precision, you should give it as 134535,67 Pa. As you have not stated that there is any dependence between number of moles and pressure, your statement is generally wrong.

[charlie1983]

You guys are great thanks for all your replies---this is a great place for assistance