Using concentrations of solutions in mols Flashcards
(6 cards)
Calculate the amount of solute in a solution from its concentration in mol/cm^3.
Amountofsolute(moles)=Concentration×Volumeofsolution
Where:
The concentration is given in moles per cubic centimeter (mol/cm³).
The volume is in cubic centimeters (cm³).
So, to find the amount of solute in moles, you multiply the concentration (mol/cm³) by the volume of the solution (cm³).
/-
calculate the concentration of a solution when it reacts completely with another solution of a known concentration.
C 1 ×V =C 2 ×V 2
C 1
is the concentration of the first solution (known concentration).
V1
is the volume of the first solution.
C2
is the concentration of the second solution (the one you’re solving for).
v2
is the volume of the second solution.
If the two solutions react in a 1:1 ratio, this equation can be used directly. However, if the ratio is different, you’ll need to adjust the formula to account for it.
describe how to carry out the titrations of strong acids and strong alkalis and calculate quantities in titrations involving concentrations in mol/dm3 and g/dm3
Molesofalkali
- Set up the apparatus:
Burette: Fill the burette with the strong alkali (e.g., sodium hydroxide, NaOH), making sure it’s clean and free from air bubbles. Record the initial reading.
Conical Flask: Place the strong acid (e.g., hydrochloric acid, HCl) in the conical flask, typically around 25 cm³.
Pipette: Use a pipette to measure 25 cm³ of the acid solution into the conical flask.
Indicator: Add a few drops of an appropriate indicator, such as phenolphthalein (which is colorless in acidic solutions and pink in basic solutions). - Titration Process:
Add the alkali slowly:
Start adding the strong alkali from the burette into the acid solution in the conical flask while continuously swirling the flask.
The alkali should be added slowly as you approach the endpoint, which is when the acid has been completely neutralized.
End Point:
The endpoint is reached when the indicator changes color, indicating that the acid and alkali have reacted in stoichiometric proportions.
For example, with phenolphthalein, the endpoint is reached when the solution changes from colorless to pink.
Record the final burette reading: Note the volume of alkali used to neutralize the acid.
- Calculate the concentration:
Once the endpoint is reached and the volume of the alkali used is known, you can calculate the concentration of the acid solution.
Formula for moles:
Molesofacid
=
Concentrationofacid
×
Volumeofacid(indm³)
Molesofacid=Concentrationofacid×Volumeofacid(indm³)
Similarly, for the alkali:
Concentrationofalkali
×
Volumeofalkali(indm³)
Molesofalkali=Concentrationofalkali×Volumeofalkali(indm³)
4. Determine the concentration of the unknown solution:
If you know the concentration of the alkali (NaOH), you can use the mole ratio from the balanced chemical equation to find the concentration of the acid.
For a typical reaction between a strong acid (HCl) and a strong alkali (NaOH), the equation is:
HCl(aq)
+
NaOH(aq)
→
NaCl(aq)
+
H
2
O(l)
HCl(aq)+NaOH(aq)→NaCl(aq)+H
2
O(l)
This is a 1:1 ratio. So, the moles of acid will be equal to the moles of alkali.
From the titration data (the volume of alkali used and its concentration), you can calculate the moles of alkali, and then use the 1:1 ratio to find the moles of acid.
Finally, use the volume of acid and its moles to calculate the concentration of the acid.
explain how the concentration of a solution in mol/dm3 is related to the mass of the solute and the volume of the solution.
Concentration(mol/dm³)
The concentration of a solution in mol/dm³ (moles per cubic decimeter) is a measure of how much solute is dissolved in a given volume of solution. The relationship between the concentration in mol/dm³, the mass of the solute, and the volume of the solution can be described by the following formula:
Amountofsolute(mol)
Volumeofsolution(dm³)
Concentration(mol/dm³)=
Volumeofsolution(dm³)
Amountofsolute(mol)
Where:
Concentration is in moles per cubic decimeter (mol/dm³).
Amount of solute is in moles (mol).
Volume of solution is in cubic decimeters (dm³).
To calculate the amount of solute from the concentration:
You can rearrange the equation to find the amount of solute (in moles):
Concentration(mol/dm³)
×
Volumeofsolution(dm³)
Amountofsolute(mol)=Concentration(mol/dm³)×Volumeofsolution(dm³)
To calculate the mass of solute:
The amount of solute is often given in moles, but if you want the mass of the solute in grams (g), you need to use the molar mass of the substance. The molar mass is the mass of one mole of a substance, expressed in grams per mole (g/mol).
Amountofsolute(mol)
×
Molarmass(g/mol)
Massofsolute(g)=Amountofsolute(mol)×Molarmass(g/mol)
Example:
Let’s say we want to calculate the mass of sodium chloride (NaCl) needed to prepare a solution of concentration 0.5 mol/dm³ in a total volume of 2 dm³.
Step 1: Calculate the moles of NaCl.
From the formula for concentration:
Concentration(mol/dm³)
×
Volume(dm³)
MolesofNaCl=Concentration(mol/dm³)×Volume(dm³)
MolesofNaCl
=
0.5
mol/dm³
×
2
dm³
=
1
mol
MolesofNaCl=0.5mol/dm³×2dm³=1mol
Step 2: Calculate the mass of NaCl.
The molar mass of NaCl is:
Sodium (Na) = 23 g/mol
Chlorine (Cl) = 35.5 g/mol
Molar mass of NaCl = 23 + 35.5 = 58.5 g/mol
Now calculate the mass of NaCl:
MolesofNaCl
×
MolarmassofNaCl
MassofNaCl=MolesofNaCl×MolarmassofNaCl
MassofNaCl
=
1
mol
×
58.5
g/mol
=
58.5
g
MassofNaCl=1mol×58.5g/mol=58.5g
So, you would need 58.5 grams of NaCl to make 2 dm³ of a 0.5 mol/dm³ NaCl solution.
Summary:
The concentration of a solution in mol/dm³ tells you how many moles of solute are in a given volume of solution.
To find the mass of the solute, you first calculate the number of moles from the concentration and volume, and then multiply by the molar mass of the solute.
The equation to remember is:
Concentration(mol/dm³)
=
Amountofsolute(mol)
Volumeofsolution(dm³)
Concentration(mol/dm³)=
Volumeofsolution(dm³)
Amountofsolute(mol)
explain what the volume of one mole of any gas at room temperature is
Volume(dm³)
At room temperature (around 20°C to 25°C) and standard atmospheric pressure (1 atmosphere or 101.3 kPa), one mole of any gas occupies a volume of approximately 24 dm³.
This volume is referred to as the molar volume of a gas, and it is true for all ideal gases under these specific conditions.
Why is this the case?
The volume of a gas is directly affected by the temperature and pressure at which it is measured, according to Boyle’s Law (for pressure and volume) and Charles’s Law (for temperature and volume).
At standard temperature and pressure (STP), defined as 0°C (273.15 K) and 1 atm, one mole of any ideal gas occupies 22.4 dm³. However, at room temperature (around 20°C), the volume increases slightly, and one mole of gas takes up about 24 dm³.
This is a useful approximation for solving problems involving gases in chemistry!
Key Points:
Room temperature = 20°C to 25°C.
Standard pressure = 1 atm (or 101.3 kPa).
Volume of 1 mole of gas at room temperature ≈ 24 dm³.
If you need to calculate the volume of a gas at room temperature and you know the number of moles, you can simply use the relationship:
Numberofmoles
×
24
dm³/mol
Volume(dm³)=Numberofmoles×24dm³/mol
This is valid for ideal gases under typical conditions at room temperature and pressure!
calculate the volume of gas at room temperature and pressure from its mass and relative formula mass. gcse aqa chem.
Volumeofgas(dm³)
To calculate the volume of a gas at room temperature and pressure (around 20°C to 25°C and 1 atm) from its mass and relative formula mass, you can follow these steps:
Formula to use:
Volumeofgas(dm³)
=
Massofgas(g)
Relativeformulamass(g/mol)
×
24
dm³/mol
Volumeofgas(dm³)=
Relativeformulamass(g/mol)
Massofgas(g)
×24dm³/mol
Where:
Mass of gas (g) is the mass of the gas you have.
Relative formula mass (g/mol) is the molar mass of the gas (the sum of the atomic masses of all atoms in the molecule).
24 dm³/mol is the molar volume of gas at room temperature and pressure (assuming ideal gas behavior).
Steps:
Calculate the number of moles of the gas.
The number of moles is given by:
Numberofmoles
=
Massofgas(g)
Relativeformulamass(g/mol)
Numberofmoles=
Relativeformulamass(g/mol)
Massofgas(g)
Calculate the volume of the gas using the relationship between moles and volume at room temperature and pressure:
Numberofmoles
×
24
dm³/mol
Volumeofgas(dm³)=Numberofmoles×24dm³/mol
