In an experiment, hydrochloric acid reacted with different volumes of sodium thiosulfate in water. A yellow precipitate was formed during the reaction. A cross drawn at the base of each flask became gradually invisible due the formation of this yellow precipitate. The time taken for the cross to become invisible was recorded. A partial record of the experiment is shown.

Based on your knowledge of factors that affect the rates of chemical reactions, predict the trend in the last column of the experimental record. Use complete sentences to explain the trend you predicted. You do not have to determine exact values for time; just describe the trend you would expect (increase or decrease) and why it occurs.

The time taken for the reaction to go to completion(time taken for the cross to disappear) decreases steadily down the column for time.

Explanation:

If we look at the table closely we would quickly observe the following;

1) the volume of HCl was held constant

2) the volume of sodium thiosulphate was increased steadily

3) the volume of water was decreased steadily

The increase in volume of thiosulphate and decrease in the volume of water meant that reactant concentration was increased steadily. From our knowledge of factors that affect the rate of reaction, we know that the rate of reaction (typically read off as time taken for a given reaction to go to completion, in this case, decrease in the time taken for the cross to disappear) increases with increase in concentration of reactants.

Hence it is expected that as the concentration of reactants increase, the rate of reaction increases. As the rate of reaction increases, the time taken for the cross to disappear decreases. Hence the answer above.

i don t now

assuming that your periodic table has eighteen columns, you should highlight   the four elements in the third column from the left of the table.

neutral atoms of elements after calcium contain d electrons. the energy of d orbitals of a particular main shell lies between the energy of the s and p orbitals of the next main shell. for example, electrons in the have energy higher than those in the orbital while lower than those of the orbital.

by the aufbau principle, electrons fill orbitals one at a time, starting from those of the lowest energy. the orbital is therefore filled right after orbitals and before orbitals.  

potassium has electron configuration and calcium . the s orbital of a main shell holds a maximum of two electrons. the next element would thus have the electron configuration and satisfy the requirements.

a neutral atom of the element contains three electrons on top of the most recent noble gas element. it should thus be placed in the third column of the periodic table. both scandium and yttrium would satisfy the conditions. an aufbau diagram indicates that the 4f orbital is filled before the 5d. however, it appears that exceptions exists for both lanthanum and actinium. neutral atoms of the two d-block elements also demonstrate the and should be highlighted as well.