Ficará correta se X, Y e Z forem substituídos, respectivamente, por:
A
2; Na2O e BaHCO3
B
2; Na2CO3 e BaCO3
C
2; Na2CO3 e Ba2CO2
D
3; Na2O e BaCO3
E
3; Na2O3 e BaHCO3
Gabarito:
2; Na2CO3 e BaCO3
Resolução:
Primeiro, devemos analisar a decomposição do bicarbonato de sódio (NaHCO3):
Visto que temos os compostos CO2 e H2O no produto, quem ainda não apareceu foi o sódio (Na). O aquecimento dessa reação faz com que o bicarbonato de sódio se decomponha em carbonato de sódio:
Em seguida, precisamos fazer o balanceamento da reação:
Na reação 2, do dióxido de carbono com o hidróxido de bário, teremos:
Como houve formação de água, podemos assumir que o hidrogênio da hidroxila do hidróxido de bário formou água, não sendo possível formar o bicarbonato de bário.
Most people can remember a phone number for up to thirty seconds. When this short amount of time elapses, however, the numbers are erased from the memory. How did the information get there in the first place? Information that makes its way to the short term memory (STM) does so via the sensory storage area. The brain has a filter which only allows stimuli that is of immediate interest to pass on to the STM, also known as the working memory.
There is much debate about the capacity and duration of the short term memory. The most accepted theory comes from George A. Miller, a cognitive psychologist who suggested that humans can remember approximately seven chunks of information. A chunk is defined as a meaningful unit of information, such as a word or name rather than just a letter or number. Modern theorists suggest that one can increase the capacity of the short term memory by chunking, or classifying similar information together. By organizing information, one can optimize the STM, and improve the chances of a memory being passed on to long term storage.
When making a conscious effort to memorize something, such as information for an exam, many people engage in ‘‘rote rehearsal’’. By repeating something over and over again, 2one is able to keep a memory alive. Unfortunately, this type of memory maintenance only succeeds if there are no interruptions. As soon as a person stops rehearsing the information, it has the tendency to disappear. When a pen and paper are not handy, people often attempt to remember a phone number by repeating it aloud. If the doorbell rings or the dog barks to come in before a person has the opportunity to make a phone call, he will likely forget the number instantly. 3Therefore, rote rehearsal is not an efficient way to pass information from the short term to long term memory. A better way is to practice ‘‘1elaborate rehearsal’’. This involves assigning semantic meaning to a piece of information so that it can be filed along with other pre-existing long term memories.
Encoding information semantically also makes it more retrievable. Retrieving information can be done by recognition or recall. Humans can easily recall memories that are stored in the long term memory and used often; however, if a memory seems to be forgotten, it may eventually be retrieved by prompting. The more cues a person is given (such as pictures), the more likely a memory can be retrieved. This is why multiple choice tests are often used for subjects that require a lot of memorization.
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(Unisc 2016) Dentre um grupo formado por 2 Engenheiros e 4 Matemáticos, três pessoas são escolhidas ao acaso. A probabilidade de que sejam escolhidos um Engenheiro e dois Matemáticos é de