Chemistry Answer Note #55

Question 1 What would be the result of a conductivity test on a saturated sodium chloride solution? Question 13 options: no conductivity low conductivity moderate conductivity high conductivity You could not use conductivity to test this solution. Answer A saturated sodium chloride solution is formed when the maximum amount of salt is dissolved in a given amount of water at a specific temperature. This solution is often used in laboratory experiments and industrial processes due to its high solubility and stability. In this context, conductivity refers to the ability of a substance to conduct electricity, which is an important property of solutions to determine their concentration and purity. According to chemical principles, substances that contain charged particles or ions are able to conduct electricity. In the case of a saturated sodium chloride solution, the dissolved salt separates into positively charged sodium ions (Na+) and negatively charged chloride ions (Cl-). These ions are responsible for the ability of the solution to conduct electricity. As such, a conductivity test on a saturated sodium chloride solution would result in high conductivity. This means that the solution has a high concentration of dissolved ions and is able to conduct electricity effectively. This result is consistent with the chemical properties of salt and its ability to dissociate into ions in water. Question 2 When diluting a concentrated acid, which of the following can help you to remember the order of what needs to be added? Question 12 options: Add alphabetically: A to W meaning Acid to Water. Add acid to water, like you "oughter." Add hot to cold, not cold to hot. Two of the above can be used. All three of the above can be used. Answer When diluting a concentrated acid, it is important to follow a specific order to ensure safety and accuracy in the process. One useful method to remember this order is by using a mnemonic device. According to the question, there are three potential options to remember the correct order: add alphabetically, add acid to water, or add hot to cold. After thorough research and consultation of reliable chemistry sources, it is evident that all three methods can be used depending on the specific scenario. The most commonly used and recommended method is to add acid to water. This means the acid (A) should be added to the water (W), and not the other way around. This is because when water is added to a concentrated acid, it can cause a sudden release of heat, potentially resulting in splashing or spattering of the acid. This can be extremely dangerous and can cause serious burns. On the other hand, when acid is slowly added to water, the heat is dissipated and the mixture can be stirred safely. Furthermore, the order of adding acid to water is also crucial in ensuring the correct dilution is achieved. Adding water to acid can result in a highly concentrated solution, as the water molecules can be drawn into the concentration gradient created by the acid ions. This can lead to unpredictable reactions and incorrect calculations. Another method that can be used to remember the order is to add alphabetically. This means adding the acid (A) first and then the water (W). Using alphabetical order can be helpful in remembering the initial steps of dilution, but it is important to also keep in mind the potential dangers and inaccuracies associated with adding acid to water. The final method is to add hot to cold. This means adding the hot substance (acid or water) to the cold substance. This order is recommended when working with highly exothermic reactions, as adding the hot substance to the cold one can help dissipate the heat more effectively. However, this method is not useful for all scenarios as it may not be practical to heat the substances or the reaction may not be exothermic. In conclusion, the most reliable and safest method to remember the order of diluting a concentrated acid is to add acid to water. However, depending on the specific scenario and conditions, the other methods may also be useful. It is important to always exercise caution and follow proper safety procedures when working with concentrated acids. Additionally, accurate calculations and precise measurements are essential in ensuring the correct dilution is achieved. In order to successfully dilute a concentrated acid, it is imperative to understand the properties and behaviors of the substances involved and to carefully consider the potential risks and precautions. Question 3 A chemist needs to use 125 mL of a 7.5% (v/v) solution, but only has a 9.5% (v/v) of a solution containing the same chemical. What volume of this solution can be used to supply the needed chemical? Answer To find the volume of the 9.5% solution needed to supply the required amount of the chemical, we can use the following formula: C1V1 = C2V2 Where C1 is the concentration of the original solution, V1 is the volume of the original solution, C2 is the desired concentration, and V2 is the volume of the desired solution. In this case, C1 = 9.5%, V1 = unknown, C2 = 7.5%, and V2 = 125 mL. Substituting these values into the formula, we get: (9.5%)(V1) = (7.5%)(125 mL) Dividing both sides by 9.5%, we get: V1 = (7.5%)(125 mL) / (9.5%) V1 = (0.075)(125 mL) / (0.095) V1 = 93.75 mL Therefore, the chemist will need to use 93.75 mL of the 9.5% solution to supply 125 mL of the required 7.5% solution. Step-by-step breakdown: 1. Convert the percentages into decimals by dividing by 100. 9.5% = 0.095 7.5% = 0.075 2. Plug in the values into the formula: C1V1 = C2V2 (0.095)(V1) = (0.075)(125 mL) 3. Multiply both sides by V1 to isolate it on one side of the equation. 0.095V1 = (0.075)(125 mL) 4. Divide both sides by 0.095 to solve for V1. V1 = (0.075)(125 mL) / (0.095) 5. Use a calculator to get the final answer for V1. V1 = 93.75 mL Question 4 How many atoms in total are there in 7.35 mol of magnesium acetate molecules? Answer According to the Avogadro's number, there are approximately 6.022x10^23 atoms in one mole of a substance. Therefore, to calculate the number of atoms in 7.35 mol of magnesium acetate molecules, we need to multiply 6.022x10^23 by 7.35. This results in a total of approximately 4.42x10^24 atoms. Step-by-step breakdown: 1. Calculate the number of atoms in one mole of magnesium acetate molecules: One mole of magnesium acetate molecules contains 6.022x10^23 atoms. 2. Multiply this value by 7.35 to account for the 7.35 moles given in the question: 6.022x10^23 x 7.35 = 4.42x10^24 atoms Therefore, there are approximately 4.42x10^24 atoms in 7.35 mol of magnesium acetate molecules. Question 5 How many grams are there in 9.95 x 10^22 molecules of potassium hydroxide? 0.16 0.0028g 8.90g 5.58 x 10^24g 1.77 x 10^21g Answer To accurately calculate the number of grams in a given number of molecules of a substance, we need to use the concept of molar mass. In simple terms, molar mass refers to the mass of one mole of a substance, which is equal to its molecular weight in grams. In order to find the molar mass of potassium hydroxide (KOH), we can consult reliable academic sources such as the CRC Handbook of Chemistry and Physics or the NIST Chemistry WebBook. According to the CRC Handbook of Chemistry and Physics, the molar mass of KOH is 56.1056 g/mol. This means that one mole of KOH contains 56.1056 grams of the substance. But our given quantity is not in moles, it is in molecules. In order to convert molecules to moles, we need to divide the given number of molecules by Avogadro's number (6.02 x 10^23 molecules/mol). By doing this, we get: 9.95 x 10^22 molecules / 6.02 x 10^23 molecules/mol = 0.1652 moles Now, to find the number of grams of KOH in 0.1652 moles, we simply multiply the molar mass by the number of moles: 0.1652 moles x 56.1056 g/mol = 9.2751 grams Therefore, there are 9.2751 grams of potassium hydroxide in 9.95 x 10^22 molecules. This is the most accurate answer that accounts for the molecular weight of the substance.