Answer:
Example
0.5 mol of sodium hydroxide is dissolved in 2 dm3 of water. Calculate the concentration of the sodium hydroxide solution formed.
Concentration =
Concentration = 0.25 mol/dm3
Volume units
Volumes used in concentration calculations must be in dm3, not in cm3. It is useful to know that 1 dm3 = 1000 cm3. This means:
divide by 1000 to convert from cm3 to dm3
multiply by 1000 to convert from dm3 to cm3
For example, 250 cm3 is 0.25 dm3 (250 ÷ 1000). It is often easiest to convert from cm3 to dm3 before continuing with a concentration calculation.
Question
100 cm3 of dilute hydrochloric acid contains 0.02 mol of dissolved hydrogen chloride. Calculate the concentration of the acid in mol/dm3.
Reveal answer
Converting between units
The relative formula mass of the solute is used to convert between mol/dm3 and g/dm3:
to convert from mol/dm3 to g/dm3, multiply by the relative formula mass
to convert from g/dm3 to mol/dm3, divide by the relative formula mass
Remember: the molar mass is the Ar or Mr in grams per mol.
Example
Calculate the concentration of 0.1 mol/dm3 sodium hydroxide solution in g/dm3. (Mr of NaOH = 40)
Concentration = 0.1 × 40
= 4 g/dm3
A very disgusting type of lemonade
Answer: 16.32 g of as excess reagent are left.
Explanation:
To calculate the moles :
According to stoichiometry :
2 moles of require = 1 mole of
Thus 0.34 moles of will require= of
Thus is the limiting reagent as it limits the formation of product and is the excess reagent.
Moles of left = (0.68-0.17) mol = 0.51 mol
Mass of
Thus 16.32 g of as excess reagent are left.
Answer:
Option (D) freezing point depression
Explanation:
Calcium chloride is added to the roadways after a snowstorm because it reduces the freezing point of the ice. Further more, it has been observed that the calcium chloride also produces enough heat which enhances the melting of the ice as it produces an exothermic reaction.
Activation energy is the minimum amount of energy that the colliding reactant molecules must possess for the formation of products. Lower the activation energy, higher will be chance of formation of products. So activation energy is the minimum energy requirement that has to overcome for the reaction to be completed. Therefore, when in a chemical reaction the reactant molecules do not collide with required activation energy, the collisions will not be fruitful even if they are properly oriented which means that the products will not form.
Hence the correct answer will be B.) no products will be formed