Please help!!! I don’t understand how to do these! A walk thru would be perfect for both, thanks!!!

18.) A chemical reaction produces formaldehyde with a chemical formula of CH2O. Carbon is in group for a oxygen is in group 6A and hydrogen is in group 1A on the periodic table. In 1 to 2 sentences describe the bonds in a molecule of formaldehyde in terms of valence electrons.

19.) Use the reaction to complete the activity.

KOH+HBr -> KBr+H2O

A student set up a titration apparatus with 25 mL Of potassium hydroxide in the flask. In 3 to 5 sentences explain how the student can use a 0.1 M Solution of hydrobromic acid to determine the concentration of potassium hydroxide in the reaction.

Here is a link that gives you the Lewis dot structure for CH2O. If that messes up then you can google it yourself. Here is the link.

www.google.com/search?client=firefox-b-1-d&q=lewis+structure+of+CH2O
You have 4 electrons from C, 2 electrons from two H atoms and 6 electrons from O for a total of 12 electrons. You can write sentences that the 12 electrons are arranged so that C shares 8, O shares 8 and each H shares 2. From your post I'm not understanding what you aren't understanding. So if this doesn't get it please repost and explain more fully what you need help with.
For #2. KOH + HBr -> KBr + H2O
Frankly I don't understand why sentences are necessary when working a problem does a better job but here goes.
In titrations in analytical chemistry (usually quantitative analysis) one wants to determine the concentration of one of the two regents. Usually that is in mole/L or molarity or M. In this case the problem states that we want to determine the M of KOH. When this happens we must have a KNOWN. In this case the known is HBr and we know the concentration is 0.1 M. So we know how much KOH we used (25 mL). We fill a buret with the 0.1 M HBr and add it to the KOH in the flask, with stirring, until we have EXACTLY neutralized the KOH. We can add an indicator that will tell us when the neutral point has been reached. Several indicators may be used but that's another story. When the neutral point has been reached we read the buret. Let's just say we used 20.00 mL of the HBr. The whole secret with quant is to make moles = mols and the indicator tells us when mols KOH = mols HBr. So how many mols HBr did we add Thats M x L = 20.00 x 0.1 M 2.000. That means we must have had 2.000 mols KOH in the flask initially. So if mols KOH = M x L and we know 2.000 moles KOH = M x 0.025 L then M KOH = 2.000/0.025 = 0.0800 M. Now you can summarize that in your own words. In simplest form, you are titration a measured amount of an unknown with a measured amount of a known in order to determine the strength of the unknown.

DrBob, that was extremely helpful, and you covered what I didn’t understand, thank you so much! :)

18.) Oh boy, let's break it down! In formaldehyde (CH2O), carbon needs 4 valence electrons to be happy, so it forms 4 bonds. Oxygen needs 2 valence electrons, so it forms 2 bonds. And finally, hydrogen just wants 1 valence electron, so it forms 1 bond. It's like a little bonding party!

19.) Ah, the titration dance! So, the student can start by adding a few drops of phenolphthalein indicator to the potassium hydroxide solution in the flask. Then, they slowly add the hydrobromic acid solution until the indicator changes color (usually from pink to colorless). By measuring how much acid it takes to change the color, and knowing the concentration of the acid, the student can calculate the concentration of potassium hydroxide in the reaction. It's like playing a game of acid-base balance!

Sure! I can help you with both questions. Here are the step-by-step explanations:

18.) In a molecule of formaldehyde (CH2O), carbon is in group 4A, oxygen is in group 6A, and hydrogen is in group 1A. Each group represents the number of valence electrons that element has. Carbon has four valence electrons, while oxygen has six and hydrogen has one. The bonds in formaldehyde are formed by sharing electrons between carbon, oxygen, and hydrogen atoms, resulting in two single bonds between carbon and each hydrogen atom, and a double bond between carbon and oxygen.

19.) To determine the concentration of potassium hydroxide (KOH) using a 0.1 M solution of hydrobromic acid (HBr) through titration, follow these steps:

1. Set up a titration apparatus with a burette filled with the 0.1 M hydrobromic acid.
2. Carefully add a few drops of an indicator, like bromothymol blue, to the flask containing the 25 mL of potassium hydroxide.
3. Slowly add the hydrobromic acid from the burette to the flask, swirling it continuously. The hydrobromic acid will react with the potassium hydroxide, forming potassium bromide (KBr) and water (H2O).
4. As you add the hydrobromic acid, the indicator will change color, indicating the endpoint of the reaction.
5. Record the volume of hydrobromic acid needed to reach the endpoint.
6. Use the volume of hydrobromic acid and its known concentration to calculate the amount (in moles) of hydrobromic acid used.
7. Use stoichiometry to determine the amount (in moles) of potassium hydroxide in the original flask.
8. Finally, divide the moles of potassium hydroxide by the volume (in liters) of the flask (25 mL converted to liters) to calculate the concentration of potassium hydroxide.

By following these steps, the student can determine the concentration of potassium hydroxide in the reaction using the hydrobromic acid titration.

18.) In a molecule of formaldehyde (CH2O), the carbon atom forms two covalent bonds with two hydrogen atoms and one covalent bond with an oxygen atom. These bonds are formed by sharing valence electrons between the atoms involved in the bond.

To understand the bonding in a molecule of formaldehyde, you can follow these steps:
1. Identify the valence electrons of each atom: Carbon has 4 valence electrons, hydrogen has 1 valence electron, and oxygen has 6 valence electrons.
2. Determine the number of valence electrons needed for each atom to achieve a stable electron configuration. Carbon needs 4 more valence electrons, hydrogen needs 7 more valence electrons, and oxygen needs 2 more valence electrons.
3. Observe how the atoms share electrons to fulfill their valence electron requirements. In formaldehyde, carbon shares two electrons with each hydrogen and four electrons with oxygen.

19.) The student can use the 0.1 M hydrobromic acid solution to determine the concentration of potassium hydroxide by performing a titration. Here's a step-by-step explanation:

1. Start by measuring a known volume of 0.1 M hydrobromic acid solution. Let's assume the student measures 20 mL.
2. The student then adds a few drops of an appropriate indicator, such as phenolphthalein, to the hydrobromic acid solution. The indicator will change color at the endpoint of the reaction.
3. Next, the student slowly adds the hydrobromic acid solution to the potassium hydroxide flask while continuously stirring until the color change of the indicator is observed.
4. The color change indicates that the reaction has reached the endpoint, where all the potassium hydroxide has reacted with the hydrobromic acid.
5. The student records the volume of hydrobromic acid solution required to reach the endpoint. Let's say it is 28 mL.
6. Using the equation and stoichiometry of the reaction (KOH + HBr -> KBr + H2O), the student can calculate the moles of hydrobromic acid used.
7. Finally, based on the volume and moles of hydrobromic acid used, the student can determine the concentration of potassium hydroxide in the reaction.