Chemistry

A) determine the mass of sodium hydroxide needed to prepare 100ml of 0.5M standard solution
B) describe the procedure used to prepare the standard solution
C) use the 100ml stock solution of 0.5M sodium hydroxide to neutralize H2SO4 by volumetric analysis I) Calculate the average volume of H2SO4
II)State the PH indicator used to the acid base reaction
III) Explain how rough titration is done
IV) Calculate the concentration of H2SO4 that can be neutralised by 25cm3 of 0.5M of sodium hydroxide

A) To determine the mass of sodium hydroxide needed to prepare a 0.5M standard solution, we need to calculate the number of moles required.

The formula for calculating the moles of a substance is:

moles = concentration (M) x volume (L)

Given that the desired concentration is 0.5M and the volume is 0.1L (since 100ml is equal to 0.1L), we can use the formula:

moles = 0.5M x 0.1L = 0.05 moles

Now, to calculate the mass of sodium hydroxide, we need to use its molar mass, which can be found in the periodic table.

The molar mass of sodium hydroxide (NaOH) is:
(Na) + (O) + (H) = (22.99 g/mol) + (16.00 g/mol) + (1.01 g/mol) = 39.00 g/mol

To find the mass, we multiply the moles by the molar mass:

mass = moles x molar mass = 0.05 moles x 39.00 g/mol = 1.95 grams

Therefore, you will need 1.95 grams of sodium hydroxide to prepare a 100ml 0.5M standard solution.

B) The procedure for preparing a standard solution of sodium hydroxide involves the following steps:

1. Measure and weigh the required mass of sodium hydroxide by following the calculated amount determined in the previous step.
2. Transfer the weighed sodium hydroxide to a clean and dry container.
3. Add distilled water to the container gradually, while stirring or shaking to ensure complete dissolution of sodium hydroxide. The volume of water added will depend on the final desired volume of the solution, which in this case is 100ml.
4. Once all the sodium hydroxide has dissolved, transfer the solution to a volumetric flask. Rinse the container to ensure all of the solution is transferred.
5. Add more distilled water to the volumetric flask until the solution reaches the mark on the neck of the flask (100ml in this case).
6. Carefully mix the solution by inverting or swirling the flask.
7. Label the flask with appropriate identification (e.g., 0.5M NaOH) and the preparation date.

Remember to use proper safety precautions, such as wearing gloves and eye protection when handling chemicals.

C)

I) To calculate the average volume of H2SO4, you'll need to perform a titration using the 0.5M sodium hydroxide solution. Start by accurately measuring a known volume (e.g., 25ml) of the H2SO4 solution using a pipette. Slowly add the sodium hydroxide solution from a burette until the neutralization point is reached, indicated by a color change or pH indicator. Record the volume of sodium hydroxide solution required for neutralization. Repeat the titration at least two more times and calculate the average volume of H2SO4 based on the recorded values.

II) The pH indicator used for the acid-base reaction between sodium hydroxide and H2SO4 will depend on the exact pH range you are interested in detecting. Some commonly used indicators for this reaction are phenolphthalein (pH range: 8.2-10) or methyl orange (pH range: 3.1-4.4). Select an appropriate indicator based on the expected pH range of your reaction.

III) Rough titration is the initial titration performed to estimate the approximate volume of titrant (in this case, sodium hydroxide) needed to reach the endpoint (neutralization point). It is done by adding the titrant quickly, drop by drop, while swirling the flask or beaker containing the analyte (H2SO4) until a noticeable color change or indicator change is observed, indicating the endpoint. The volume of titrant used during rough titration helps in estimating the required volume of titrant for accurate titration.

IV) To calculate the concentration of H2SO4 that can be neutralized by 25cm3 of 0.5M sodium hydroxide, we can use the balanced chemical equation and stoichiometry.

The balanced equation for the reaction between H2SO4 and NaOH is:

H2SO4 + 2NaOH → Na2SO4 + 2H2O

From the equation, we can see that one mole of H2SO4 reacts with two moles of NaOH. Since we know the concentration and volume of NaOH (0.5M and 25cm3), we can calculate the number of moles of NaOH used:

moles of NaOH = concentration (M) x volume (L)
moles of NaOH = 0.5M x 0.025L = 0.0125 moles

Since the stoichiometry ratio is 1:2 between H2SO4 and NaOH, the moles of H2SO4 will be half of the moles of NaOH:

moles of H2SO4 = 0.0125 moles / 2 = 0.00625 moles

Finally, to determine the concentration of H2SO4, divide the moles of H2SO4 by the volume (in liters) of H2SO4 used in the titration:

concentration of H2SO4 = moles of H2SO4 / volume (L) of H2SO4

Note: Make sure to convert the volume of H2SO4 (25cm3) to liters before performing the calculation.

Now you have the step-by-step explanations for each question in your chemistry problem. Good luck!