Question

]In a lab, a student dissolves 6.9 g of sodium chloride (NaCl) in 125 g of water (H2O).

What is the molality concentration of the solution?

Answer 1

Molartiy = Moles/Litres

Answer 2

Density of water is 1g/mL

Answer 3

you can mostly assume that 1g = 1mL of water but different temperatures and pressures can change this relationship

Answer 4

So how would I find the answer out? The answer choices are:

9.4 x 10-4 m

0.055 m

0.94 m

18.0 m

Answer 5

Read what I wrote

Answer 6

Moles = Grams/Molecular Mass

Answer 7

sorry forgot that formula

Answer 8

So you need to convert your grams of sodium chloride to moles

Answer 9

and convert your grams of water to litres of water

Answer 10

You know how to find molecular mass right?

Answer 11

So I would do 6.9g of sodium chloride divided by the mass of sodium chloride?

Answer 12

the molecular mass of sodium chloride (which has units g/mol)

Answer 13

So wait, would it just be the mass of Na and Cl and then add the two?

Answer 14

If I wanted to find the molecular mass of Hydrogen gas (H2)

I would look at the periodic table and find,

One hydrogen atom has a molecular mass of 1.00794g/mol

Thus, H2 gas has a molecular mass of

1.00794g/mol + 1.00794g/mol = 2.01588g/mol

Then I would just take the grams of H2 gas I had and divide it by the number I just calculated to find the moles of H2 gas I had

Answer 15

yes

Answer 16

Because if so then it would be 6.9 divided by 58.44 which is .12 then what do I do?

Answer 17

Opps forgive me

Answer 18

make sure to include units in your calculations

Answer 19

So you have 0.12moles

Now you need to convert the grams of water to litres of water

Answer 20

then use the molarity formula

Answer 21

Which would be 125 litres, right?

Answer 22

Read what I wrote above

Answer 23

1g= 1ml, so what would one ml be to one L?

Answer 24

1000 mL = 1L

Answer 25

This is stuff you need to memorize

Answer 26

If you plan on going on into sciences/engineering in post secondary

Answer 27

Just to note.

Answer 28

Well I was suppose to learn it in my chem class, but my teacher wasn't good so this is why I am in online school for chem

Answer 29

Its fine man just work hard you will get this stuff it is actually pretty simple, and you seem smart

Answer 30

https://www.youtube.com/watch?v=ScvuRb6vsz4 this might help with unit conversion

Answer 31

So it would be .125 so would I do .12 divided by .125 for the final answer?

Answer 32

yes

Answer 33

So it would be around .96 so I would go with .94 for the answer?

Answer 34

Also do you think you would have time to help me with like two other questions??

Answer 35

Maybe if they are quick I have a lot of stuff to do

Answer 36

What is the pressure, in mm Hg, of 2.50 moles of an ideal gas if it has a volume of 50.0 liters when the temperature is 27.0° C?

Answer 37

and A sample of gas has a volume of 20.0 liters at 22.0° C. If the pressure remains constant, what is the volume at 100.0° C?

Answer 38

PV=nRT

Ideal Gas law wikipedia it

Answer 39

The second one also uses Ideal gas law

Answer 40

So for the second one these are the answer choices:
15.8 liters

24.4 liters

25.3 liters

90.1 liters
Would it be the 3rd one???

Answer 41

Which means? Lol I am sorry that made no sense.

Answer 42

Look up idea gas law on wikipedia it tells you all the variables in the equation

Answer 43

You need to use it when dealing with gasses, though remember it models gasses thats constituents do not interact with each other

Answer 44

So it is not a real model it just simplifies things, because in reality (a real gas) the atoms/molecules that make it up interact with eachother

Answer 45

But that is just a side note about the law that you should know

Answer 46

Like,

\[P = n_1R_1T_1\]
\[P = n_2R_2T_2\]

Where the first equation is for the first state of the gas and the second denotes the second state of the gas

Temperature and volume are proportional
Temperature and pressure are inversely proportional
(This makes sense if you think about it, remember temperature is just kinetic movement of particles (atoms/molecules))

So since pressure is constant, P will remain the same in both equations (because it is constant or unchanging in the process of this question)

Answer 47

Opps!

There should be a V in those equations

Answer 48

\[P = \frac{n_1T_1R}{V_1}\]
\[P = \frac{n_2T_2R}{V_2}\]

Answer 49

you can set these two equations equal to each other, and cancel out the constants.

number of moles do not change so they cancel, R is always a constant so it cancels

Answer 50

Do you follow?

Answer 51

I am trying to do the first one and I am so confused on it

Answer 52

So for the first one "What is the pressure, in mm Hg, of 2.50 moles of an ideal gas if it has a volume of 50.0 liters when the temperature is 27.0° C?" n=2.5 moles T=27 and R would be equal to what?

Answer 53

R is the ideal gas constant

Answer 54

https://www.wolframalpha.com/input/?i=Ideal+Gas+constant

Answer 55

You need to use the one with the correct units

Answer 56

or else you will get the wrong answer

Answer 57

Unit conversion is very important in these questions, you need to realize when you divide two units they cancel out, for instance,


1mL/1mL = 1 (units canceled, scaler quantity now)
1mL*1g = 1g*mL
1L/2mL = 0.5L/mL
2L*g/1g = 2L

Answer 58

So which do I use for the first one???

Answer 59

Look at your units

Answer 60

If the units dont cancel out when you write out the equation then you are using the wrong gas constant

Answer 61

You should be left with units for the variable you are solving

Answer 62

Right now have is 2.5 moles times 27(temp) times R(?) divided by 50(Liters)

Answer 63

Also, if you have Celsius you need to convert to Kelvin

Answer 64

273 + Celsius = Kelvin

Answer 65

OHHHHHHHHHHHHHH!!

Answer 66

kelvin has the units K and is the Metric unit for temperature

Answer 67

I forgot to mention

Answer 68

Okay let me see if I know the answer now

Answer 69

Ok I will be back in probably 20-30 minutes I need to see if the patch on my cars tire is actually going to hold.

Answer 70

Okay

Answer 71

Back did you figure it out? Sorry for taking so long tire is working but needed to re-setup sound system so blah smeh