General Chemistry Homework Help

1 roac S Ily Neutral Solution pH of . It is said to be neutral. • This means that there are as many H* as OH. are neutral. and • Pure . is neither acidic or basic.

Buffers Substances that change_____in pH. _____H+ when pH is to low (acidic). _______H+ when pH is to high (basic).

Fill in the Blank: Element Indium In Y S Rubidium Rb Argon Yttrium Sulfur Symbol Protons 1+ Ar 37 Neutrons 50 22 Electrons Atomic Number 49 18 39 16 Atomic Mass 114 32 85

1. The number of protons represents the a. atomic mass b. atomic number c. atomic weight d. atomic Isotope 2. The number of electrons in an element equals a. the number of neutrons b. the number of protons c. the number of protons + neutrons d. the number of protons-neutrons 3. An element has an atomic number of 25. That element is a. Na b. Sr c. Mn d. Cr 4. One proper way to indicate an isotope of Si with an atomic mass of 28 is a. 28-SI b. Si-28 C. 285 28 Si d. 5. How many neutrons are in the nucleus of Mo? a. 53 b. 42 c. 48 U.S4

3) Write the expression of base dissociation constant for the following reaction point out the conjugate acid: \mathrm{NH}_{3}(\mathrm{aq})+\mathrm{H}_{2} \mathrm{O}(\mathrm{l}) \rightleftharpoons \mathrm{NH}_{4}^{+}(\mathrm{aq})+\mathrm{OH}^{-}(\mathrm{aq})

The reaction of cyclohexadiene with acrolein is shown below. Use Frontier Molecular Orbital Theory (showing relevant orbital interactions) to explain why this reaction favours the endo product 18. Explain, using energy levels, why the reaction of cyclohexadiene proceedsrapidly with acrolein than with ethene.more Explain, using energy levels, why the reaction below, between an electron-deficient diene and an electron-rich alkene, occurs readily. Draw the structure, including stereochemistry, of the product 19 of the reaction below. Draw a 'curly' arrow mechanism and draw the transition state leading to

Many metals corrode. An experiment is carried out to see if magnesium ribbon wrapped around a piece of iron rod has an effect on the rate at which the iron rod rusts. The apparatus is shown in Figure 4. The method used is an iron rod, with magnesium ribbon wrapped around it, is placed in a boiling tube labelled A 10 cm3 water from a measuring cylinder is poured into this boiling tube an identical rod but with no magnesium ribbon wrapped around it is placed in a second boiling tube labelled B Both boiling tubes are left for a few days. (i) Explain why iron rod rather than stainless steel rod is used in this experiment. (iii) After a few days the two boiling tubes were examined. (ii) State why it is not necessary to use a pipette to measure out 10 cm3 water in this experiment.

Q4) Consider the following pH curve: a) Explain if the analyte used to obtain the following pH curve was strong or weak, an acid or a base, monoprotic or polyprotic and HOW YOU KNOW (i.e.what were the give away clues.) b) What would be an appropriate indicator for this reaction? Explain why.

Into a beaker of ultrapure water, 20 mL of hexane is added. A high-speed stirrer thencauses the hexane to be distributed into a dispersion of droplets, each of radius 1 um.If the water/hexane interfacial tension is 50.2 mN m-', how much work is done indispersing the oil? What is the pressure difference between the inside and outside of each droplet?

Which drawing(s) represents a face-centered cubic unit cell?

14. The following table gives experimental boiling points for a series of compounds containing group 16 elements bonded to hydrogen atoms. a) (2 marks) Briefly explain the main reason why boiling point decreases from H2Te to H2Se to H2S. b) (1 mark) Briefly explain why H2O seemingly breaks this trend with a higher boiling point compared to most of the others.

In which reaction is nitrogen reduced? \mathrm{Cu}^{2+}+2 \mathrm{NO}_{2}+2 \mathrm{H}_{2} \mathrm{O} \rightarrow \mathrm{Cu}+4 \mathrm{H}^{+}+2 \mathrm{NO}_{3}^{-} \mathrm{Q} 4 \mathrm{Zn}+10 \mathrm{H}^{+}+\mathrm{NO}_{3}^{-} \rightarrow 4 \mathrm{Zn}^{2+}+\mathrm{NH}_{4}{ }^{+}+3 \mathrm{H}_{2} \mathrm{O} 2 \mathrm{NO}+\mathrm{O}_{2} \rightarrow 2 \mathrm{NO}_{2} 4 \mathrm{NH}_{3}+5 \mathrm{O}_{2} \rightarrow 4 \mathrm{NO}+6 \mathrm{H}_{2} \mathrm{O}

Covalent substances can be simple molecular covalent or giant covalent. Oxygen, O2, is also a simple molecular, covalent substance. Draw a dot and cross diagram for the molecule of oxygen.

Which of the following substances will be a solid at 20 °C and will melt when placed in a beaker of hot water at 80 °C?

The concentration of dilute sulfuric acid can be determined by titration with sodium hydroxide solution of known concentration. 25.00 cm of dilute sulfuric acid was measured out using a pipette and transferred to a conical flask. A few drops of methyl orange indicator were added to the acid in the conical flask. Sodium hydroxidesolution was added to the acid from a burette until the indicator changed colour. The titration was repeated until two concordant results were obtained. The accurate result was the average of the two concordant results. A brief report of the practical method has been given above. Further detail can be added to this method to ensure that anyone following the method will obtain anaccurate result. Explain two details that could be added to this practical method to ensure an accurate result is obtained.

When iron reacts with copper sulfate solution, solid copper is formed. Two possible equations for this reaction are A Cuso4, + Fe Cu + FeS04 \text { B } 3 \mathrm{CuSO}_{4}+2 \mathrm{Fe} \rightarrow 3 \mathrm{Cu}+\mathrm{Fe}_{2}\left(5 \mathrm{O}_{4}\right)_{3} It was found that 10.00 g of iron powder reacted with excess copper sulfate solution to produce 11.34 g of copper. Carry out a calculation to decide which equation, A or B, represents the reaction taking place.

A substance is heated at a constant rate and its temperature is taken every minute. During the heating, the substance undergoes one change of state. The results are shown on the graph in Figure 5. Explain the shape of the graph in terms of the changes in the movement and arrangement of the particlesas the substance is heated.

An experiment is planned to record the change in pH as a powdered base is added to 50 cm3 dilute hydrochloric acid. The method suggested is step 1add dilute hydrochloric acid up to the 50 cm³ mark on a beaker; step 2 add one spatula of the base and stir; step 3measure the pH of the mixture; step 4 repeat steps 2 and 3 until the pH stops changing. (i) State how you could change the method so that the amounts of dilute hydrochloric acid and of the base can be measured more accurately. dilute hydrochloric acid base (ii) During the experiment the pH changes from 2 to 10. If phenolphthalein indicator is added at the beginning of the experiment, a colour change occurs as the base is added. State the colour change that occurs. colour at start ... colour at end .. (iii) Explain, in terms of the particles present, why the pH increases during the experiment.