[Panzer336]

Hi I am relatively new to chemistry and got a bit of help earlier (thanks)
I have no idea in how to get the answer to these can anyone help please.

Q1
SiO2 + 4HF  SiF4 + 2H2O
How many grams of HF would i need to react with 150.0g of Silica?

Q2
What volume of a solution of HCI with a concentration of 0.25 mol.L-1, contains 0.50 mol of the HCI?

Q3
What is the molar concentration of the solute in each of the following solutions
1.55 lires containing 153g of Na2CO3?
0.25 litres containing 1.675g of Na2C2O4?

[Borek]

SiO2 + 4HF  SiF4 + 2H2O
How many grams of HF would i need to react with 150.0g of Silica?

150 g - how many moles of SiO₂?

How many moles of HF react with 1 mole of SiO₂?

[szyman63]

For 2 and 3. try these equations

Molarity = molar concentration
Volume= Liters (L)
mol = Moles

Molarity (M) = # of moles of solute
                       Volume of solution

# of moles = Molarity * Volume

put your numbers into one of these equations. here is an example to help you solve yours

You need to make an aqueous solution of 0.202 M potassium nitrate for an experiment in lab, using a 500 mL volumetric flask. How much solid potassium nitrate should you add in grams?

# of moles=x
molarity = .202
Volume = 500/1000=.5L      1 L = 1000mL

x= .202M*.5
x=.101 mol K(NO_3_)
Now to find grams you would just convert moles to grams using

# of moles * # of grams per mole

Grams per mole is the number you get when you take each element and add up their atomic masses. SO:
K= 39.10                       so: 39.10+14.01+48 = 101.11 grams per mole
N= 14.01                   
O=16*3= 48           so: .101 mol * 101.11 gmol = 10.21

so your answer will be 10.21g

[JGK]

I may be having a "senior moment" here, but I'm finding it incredible that problems like this are cropping up on the Undergraduate chemistry forum.

Even for the high school forum they could be regarded as fairly simple