Calculate the number of moles in 20g of NaOH.
Answers
Answer:
Given that 20 grams of NaOH is present in 5 liters of solution. ⇒ Number of moles which make up 20 grams of NaOH = (20 grams × 1 Mole)/(40 grams) = 0.5 moles.
Explanation:
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Answer:
20 gr of NaOH correspond to 0.5 moles which are contained in 0.5 liter of solution.
Explanation:
20 gr of NaOH correspond to 0.5 moles which are contained in 0.5 liter of solution.
given that, 60gNaOH
Molar mass =23+16+1=40g/mol
Moles = MolarMass/gramweight
= 40/60 = 1.5moles
Is it possible to obtain 2 liters of a solution of NaOH (Mw = 40) 1 M by diluting a solution containing 0,2 grams of NaOH in 100 ml of solution ?
In order to prepare 2 liters of a 1 M solution we need 2 moles of NaOH, i.e. 80 grams.
Therefore, we need to calculate the volume of the 0.2% solution of NaOH containing 80 grams of NaOH.
This volume can be calculated as follows:
0,2 : 100 = 80 : v
v = (80)(100)/0.2 = 40000 ml = 40 liters
Therefore it is not possible to prepare the solution.
2. How many water you have to add to 450 ml of a solution 0.3 M to obtain a concentration 0.25 M ?
This problems can be easily solved by rembering that MiVi = MfVf and thus
(0.45)(0.3) = (0.25)(Vf)
(0.45)(0.3)
Vf = ------------- = 0.54 liter = 540 ml
(0.25)
Therefore the water to add is 540 - 470 = 70 ml. Alternatively we can observe that the initial concentration is 0.3/0.25 = 1.2 times more concentrated than the final one. It follows that the volume of the final (diluted) solution should be (450) (1.2) = 540 ml.
3. The molecular weight (mw) of HCl is 36, calculate: i) the grams of HCl contained in 0.2 moles; ii) the grams of HCl needed to prepare 500 ml of a solution 1 M.
i) moles are given by grams/molecular weight, thus
(moles) (mw) = (36) (0.2) = 7.2 grams
ii) a solution 1 M contain 1 mole/liter thus 36 grams/liters. It follows that for 500 ml we need:
36/2 = 18 grams
4. 500 ml of a solution contains 20 grams of NaOH (mw = 40). Calculate the molarity of the solution.
20 gr of NaOH correspond to 0.5 moles which are contained in 0.5 liter of solution. In one liter of solution there will be (2)(0.5) = 1 mole and thus the solution is 1 M.
5. A solution of NaOH (mw = 40) is prepared by dissolving 20 grams of the base in enough water to make one liter of solution. Calculate the molarity of this solution.
the moles present in 20 gr of NaOH are:
moles = gr/mw = 20/40 = 0.5 moles
Since molarity is the number of moles in 1 liter of solution, the solution is 0.5 molar.
6. Calculate the grams of NaCl (mw = 58) contained in 30 ml of a 0.2 M solution.
A 0.2 M solution contains 0.2 moles/liter and remembering that moles = grams/mw
grams = (moles) (Mw) = (0.2) (58) = 11.6 grams of NaCl
Now we can compute the grams in 30 ml with the following proportion
11.6 : 1000 = x : 30
x = (11.6) (30)/1000 = 0.348 grams of NaCl
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