Which one of the ff is correct about Acids?

How many grams of Na2s do we need to dissolve in 200ml of water to get a solution that is 0.2 M?

DochEvi [55]

We know that the molarity of a solution is calculated by the following equation:

$Molarity = \frac{# moles}{L}$

That being said we are given two of the 3 things that we need: Volume of water, as well as the molarity of the solution. Let's plug those in to the equation to find how many moles of $Na_{2}S$ that we need:

$0.2 M = \frac{moles}{0.2 L}$ => $moles =0.04$

This means that we have 0.04 moles of $Na_{2}S$ .

In order to calculate the number of grams that we need for this solution, we must first calculate how many grams of $Na_{2}S$ are in 1 mole. We do this by taking the atomic masses of each element from the periodic table and adding them together.

Na = 22.99 g
S = 32.06 g

We have 2 Na's, and we have 1 S. So lets add them together:

2(22.99) + (32.06) = $\frac{78.04g}{mol}$ .

Since we need 0.04 moles of $Na_{2}S$ , we can multiply the molar weight of the molecule times the amount of moles needed to find the total grams that we need for the solution:

$\frac{78.04g}{mol}*0.04 moles = 3.1216 g$

Now we know that in order to make a 0.2 M solution of $Na_{2}S$ , we must use 3.1216 grams.

4 0

4 years ago

A solution is made by dissolving 21.5 grams of glucose (C6H12O6) in 255 grams of water. What is the freezing point depression of

Dafna1 [17]

Remember the vital equations for this:
(freezing point depression) = (Depression Constant) * (molality of solution)
Molality = (moles of solute) / (kg of solvent)
Step 1: Find molar mass of glucose
6 carbon * (12.01 g/mol) + 12 hydrogen * (1.01 g/mol) + 6 oxygen (16.00 g/mol)
= 180.18 g/mol
21.5 g glucose * (1 mole glucose / 180.18 g glucose) = 0.119 moles of glucose
Step 2: Convert grams of solvent to kilograms of solvent
255 g H2O * (1 kg/1000g) = 0.255 kg H2O
Step 3: Find the molality of the solution
molality = (moles solute)/(kg solvent)
molality = (0.119 moles glucose)/(0.255 kg H2O solvent) = 0.468 m (molal)
Step 4: Plug into depression equation
FP-depression = (-1.86°C/m) * (0.468 m) = -0.870 <span>°C</span>

3 0

3 years ago

Use one of your experimentally determined values of k, the activation energy you determined, and the Arrhenius equation to calcu

stealth61 [152]

Answer:

Explanation:

Use one of your experimentally determined values of k, the activation energy you determined, and the Arrhenius equation to calculate the value of the rate constant at 25 °C. Alternatively, you can simply extrapolate the straight line plot of ln(k) vs. 1/T in your notebook to 1/298 , read off the value of ln(k), and determine the value of k. Please put your answer in scientific notation. slope=-12070, Ea=100kJ/mol, k= 0.000717(45C), 0.00284(55C), 0.00492(65C), 0.0165(75C), 0.0396(85C)

Explanation;

According to Arrhenius equation:

i.e. ln(k2/k1) = -Ea/R (1/T2 - 1/T1)

Where, k1 = 0.000717, T1 = 45 oC = (45+273) K = 318 K

T2 = 25 oC = (25 + 273) K = 298 K

i.e. ln(k2/0.000717) = -12070 (1/298 - 1/318)

i.e. ln(k2/0.000717) = -2.54738

i.e. k2/0.000717 = $e^{-2.54738}$

= 0.078286

Therefore, the required constant (k2) = 0.078286 * 0.000717 = $5.61*10^-^5$

6 0

3 years ago

Calculate the energy of a photon of radiation with a frequency of 9.3x10^14Hz

Yuki888 [10]

Answer:

10.5!!!!!!!!!!!!!!!!!!!!!!

3 0

3 years ago

Which of the following is used to calculate the distance to a star based on subtle shifts in the star's position relative to an

Nana76 [90]

Parrallax is used to calculate the distance.

8 0

4 years ago